GB2051850A - Nematic liquid crystal compositions for display devices - Google Patents

Abstract

A nematic liquid crystal composition for use in display devices comprises (a) at least one compound of the formula: <IMAGE> (b) at least one compound of the formula: <IMAGE> (c) at least one compound of the formula: <IMAGE> and/or <IMAGE> wherein R1 and R2 are alkyl, alkoxy or alkanoyl, R3 is alkyl, alkoxy or alkanoyloxy, Y is CN or NO2, R5 and R6 are alkyl, alkoxy, alkanoyl, alkanoyloxy or alkoxycarbonyloxy and m is an integer of 1-10, the various hydrocarbon chains being straight chains of 1-10 carbon atoms. The composition, which may contain one or more additional nematic liquid crystal compounds having positive dielectric anisotropy and/or their homologous compounds, and/or one or more nematic liquid crystal compounds having negative dielectric anisotropy and/or their homologous compounds, is colourless, chemically stable and well suited for use in multiplexed displays; it has a broad mesomorphic range and a fast response speed.

Description

SPECIFICATION Nematic liquid crystal materials for display devices This invention relates to a nematic liquid crystal composition used for display devices, particularly those of a multiplexing drive system.

It is said that most desirable ones of the liquid crystal materials (including compounds and compositions) used for field-effect type liquid crystal display elements such as for example twisted nematic type (TN type) liquid crystal display elements are those which meet the following three requirements: First requirement: good adaptability to the orientation controlling section.

Second requirement: operability over a wide temperature range.

Third requirement: good responsiveness over a wide temperature range, particularly at low temperatures.

Regarding the first requirement, it is of paramount importance for the structure of the display element to control the molecular arrangement such that the molecules of the liquid crystal compound will be oriented parallel to each other and in one direction at the interfaces of the upper and lower plates which hold the molecules. Such control has been accomplished heretofore by forming a SiO film at the interface by oblique vacuum vaporization, or by rubbing techniques.

As for the second requirement, it is the minimum requirement that the material is liquid crystal at around normal temperature (25oC), but practically, it is required that the material presents a liquid crystal condition in the temperature range of -9 O"C to about +600C or higher.

As for the third requirement, there has been studied to find out liquid crystal materials having a low viscosity as well as satisfying the first and second requirements mentioned above.

On one hand, various types of liquid crystal materials for display elements, particularly those of a multiplexing drive system, such as Schiff base type, ester type, biphenyl type, azoxy type, etc., have been proposed to date. The azoxy type liquid crystal materials have excellent temperature characteristics (small in AT), that is, they are very limited in variation of threshold voltage with change of temperature and, as explained later, they provide an operational margin M of greater than 10% under the 1/3 bias and 1/3 duty multiplexing drive conditions. Theazoxy liquid crystal materials are represented by the following general formula:

They possess per se weakly negative dielectric anisotropy and are usually used as a mixed system with a nematic liquid crystal compound having positive dielectric anisotropy (Np).But these azoxy type liquid crystal materials are colored (in yellow) as they absorb a part of visible light Also, they show the maximum light absorption at 350 nm and undergo the following photochemical reaction owing to the wavelength around such level:

A non-liquid crystal compound is produced by such photochemical reaction and this new product changes the color of the liquid crystal from yellow into red. Usually, electric resistance of the liquid crystal is also sharply lowered. Therefore, in actual use of such azoxy type nematic liquid crystals, it needs to adapt a 500 nm cut filter in the device (element) so as to avoid photo-deterioration that might be caused by the sunlight or fluorescent light. This naturally complicates the mechanism of the device (element).

Other types of liquid crystals which are resistant to such photo-deterioration, such as Schiff base type, biphenyl type, ester type, etc., have been noticed for their availability as white display material and their adaptation to the display devices has been debated.

The biphenyl type liquid crystals are credited with high chemical stability as they are highly resistant to light, water and oxygen. However, most of the known biphenyl type materials which form liquid crystal at room temperature are the ones having positive dielectric anisotropy, and a few are known of the negative equivalents which are liquid crystal at room temperature and practically useful.

Therefore, there are only a few kinds of liquid crystal compounds which can form a mixed system with biphenyl type alone. Also, because of not so high value of positive dielectric anisotropy, wide range adjustment of threshold value is hardly possible with these materials, and further, such threshold voltage has high temperatures dependency (large in AT), so that these materials are generally considered unsuited for multiplexing drive.

The ester type liquid crystal compounds have relatively good chemical stability and there are known many kinds of single liquid crystal compounds of positive or negative dielectric anisotropy.

However, threshold voltage of these compounds has relatively high temperature dependency and their viscosity is also considerably high, so that generally these compounds can hardly meet the afore-said second and third requirements.

The Schiff base type liquid crystal compounds have better properties than the ester type, but because of strong hydrolytic disposition, matching with the packing portion of the display element is often required for their use.

Individual liquid crystal materials are disclosed in, for example, U.S. Patent Nos. 4,137,192 and 4,147,651, Molecular Crystals and Liquid Crystals 22, 285-299 (1973), J. Org. Chem. 38, 3160-3164 (1973), East German Patent No. 105,701, etc., but their special combinations are not known yet.

On the other hand, there have been studied various liquid crystal materials for TN type liquid crystal display elements. These liquid crystal materials can be divided into two groups, one of which consists of liquid crystal materials having positive dielectric anisotropy (Np type liquid crystal materials) and the other of which consists of a mixture of liquid crystal materials having negative dielectric anisotropy (Nn type liquid crystal materials) and Np type liquid crystal materials. In the former case, since the kinds of single liquid crystals having positive dielectric anisotropy are not so large and their mesomorphic ranges (MR) are narrow, it is almost impossible to obtain mixtures of these liquid crystal materials having wide MR, even if these liquid crystal materials are mixed each other.Further, since a mixture of Np type liquid crystal materials alone has a high viscosity due to assembly of molecules of strong polarity, it generally has a defect in that responsiveness is lowered when applied to a TN type liquid crystal display element, or the like.

In order to overcome such a defect, there have been made a very few proposals, for example, a proposal for improving temperature dependency of threshold voltage, which is a defect of biphenyl type liquid crystals, by mixing a Np type liquid crystal of the formula:

having a wide MR by itself with a biphenyl type Np type liquid crystal having a relatively low viscosity.

But, when a large amount of such a material having a long molecular chain is added, there arise undesirable side effects such as the viscosity is increased, elestic constant is increased, the threshold voltage value is increased, the angle dependency of threshold voltage (AO) is worsened, and the like.

Thus the study of the mixture of Np type liquid crystal materials alone seems to be fruitless in the development of materials for multiplexing drive.

On the contrary, there have been many proposals as to mixtures of Nn and Np type liquid crystal materials. Many of these proposals aim at obtaining liquid crystal materials having a wide MR or a low viscosity. Only a limited number of proposals aim at giving or maintaining multiplexing drive properties.

For example, there is a proposal of a mixture of nun and Np type liquid crystal materials wherein an azoxy series liquid crystal is used as an Nn type liquid crystal and an ester series liquid crystal such as 4cyanophenyl-4'-substituted benzoate, or a biphenyl series liquid crystal such as 4-cyano-4'-substituted biphenyl as an Np type liquid crystal. Among these proposals, some of them indicate importance of temperature characteristics of threshold voltage and rise properties of brightness, and rare cases, importance of angle dependency of threshold voltage, for improving multiplexing drive properties.But there have scarceiy been proposals which evaluate quantitatively individual properties mentioned above in relation to structures, physical properties, etc. of liquid crystal materials systematically and suggest which liquid crystal materials are suitable for giving excellent multiplexing drive properties to the mixture of Nn and Np type liquid crystal materials. Further, there has been no proposal as to liquid crystal materials for multiplexing drive satisfying not only display properties but also other conditions relating to reliability which is important in practical use, taking chemical stability also into consideration.

It is an object of this invention to provide a colorless liquid crystal composition which is excellent in chemical stability and multiplexing drive properties. It is another object of this invention to provide a liquid crystal composition which is practically valuable with satisfying various requirements such as being chemically stable and colorless, being able to be oriented stably in a wide temperature range, having a wide operational margin, having a fast response speed, and the like.

A mixed system comprising at least one Nn type 4-substituted phenyltrans(equatorial-equatorial)cyclohexyl carboxylate of the formula:

wherein R, is n-CrnH 2m+1' nCmH2m+O, or n-C mH2m+i-CO; R2 is n-CqH 2q+1' n-CqH2q+1-0 or n-CqH2q+1-CO; m and q are each integrer of 1 to 10; and n is a symbol indicating that the carbon chain is straight, and at least one Np type 4t-substituted-4-cyanobiphenyl of the formula:

wherein R3 is n-CrH 2r+1' n-CrH2r+i-O or n-CrH2r+i-COO; Y is CN or NO2; r is an integer of 1 to 10; and n is as defind above, can satisfy the second requirement mentioned above.In the formula (I), the bond between the carbon atom of the cyclohexane ring and the carbon atom of the carbonyl group is an equatrial bond. The above-mentioned mixed system of Nn and Np type liquid crystals is excellent in responsiveness and other electro-optical properties, but in order to broaden practical utility in a wide temperature range, it is preferable to add at least one third component of the formula:

wherein R5 is n-CmH2m+1'-O,n-CmH2m+1-Co,n-CmH2m+1-COO,or n-CmH2m+1-OCOO;R6 is n-C@H20+1'n-C@h20+1-O@n-CH@@@-CO.n-CH@@@-COO@@ n-CqH2q+1OCOO; m and q are each integer of 1 to 10, and/or at least one compound of the formula:

wherein m is an integer of 1 to 10.

The liquid crystal composition comprising at least one Nn type liquid crystal of the formula (I), at least one Np type liquid crystal of the formula (II), and at least one third component of the formula (III) and or (IV) mayfurther contain one or more forth and fifth components as explained hereinafter.

In the accompanying drawings: Figure 1 is a sectional view showing an example of liquid crystal display element.

Figure 2 is a structural diagram showing the orientation pattern of liquid crystal molecules.

Figure 3 shows an example of multiplexing drive waveforms according to the voltage-averaging method (1/3 bias).

Figure 4 is a diagram showing the brightness-voltage characteristics at multiplexing drive.

Figure 5 is a drawing showing the definition of viewing angle.

Figure 6 is a schematic view of an apparatus for measuring the electro-optical properties of the composition.

Figure 7 shows the 1/3 bias, 1/3 duty driving waveforms.

Figure 8 shows the 1/2 bias, 1/2 duty driving waveforms.

Figure 9 is a diagram showing relationship between temperature characteristics (AT) and viscosity of various liquid crystals.

Figure 10 is a phase diagram of a Schiff base type liquid crystal.

Figures 11, 12 and 13 are phase diagrams of mixed liquid crystals of this invention.

Figure 14 is a characteristic diagram showing the relation between Np/Nn mixing ratio and Vth.

Figures 15 and 16 are drawings showing response time of various liquid crystals.

Figures 17 and 18 are drawings showing refractive index anisotropy of mixed liquid crystals of this invention.

Before describing the respective components of the composition of this invention, detailed explanations are given to TN type liquid crystal display elements and the afore-said three requirements for practical liquid crystal materials.

Fig. 1 shows an example of twisted nematic type (TN type) liquid crystal display elements which are among the field-effect type liquid crystal display elements. The liquid crystal display element shown in Fig. 1 comprises a first substrate 1 and a second substrate 2 both of which are made of transparent glass or other like material and arranged substantially parallel to each other with a predetermined spacing, for example 5 to 15 m, and sealed at the periphery with a sealant 3 such as glass frit or an organic adhesive, and a nematic liquid crystal 4 encapsulated therein. The predetermined spacing may be provided by placing a spacer 5 made of fiber glass, glass powder or such. The sealant 3 may be so designed as to doub!e as spacer.

Electrodes 6 of a predetermined pattern are formed on the internal opposing sides of said first and second substrates 1 and 2, and the faces contacted with the liquid crystal are worked into liquid crystal controlling planes 7 and 8 where the liquid crystal molecules in the vicinity of these planes are oriented in a given direction. Such orientation controlling planes can be formed by coating the electrode-carrying side of each substrate with an oblique vacuum vaporization film of SiO or with an organic highmolecular film or a film of an inorganic material, and rubbing the coated surface in a given direction with cotton or other means.

The liquid crystal orientation controlling planes 7 and 8 of the first and second substrates 1 and 2 are differentiated in the liquid crystal orienting direction so that the molecules of the nematic liquid crystal 4 disposed between said both substrates 1 and 2 will be oriented twistedly from one direction (first direction on the controlling plane 7) to the other direction (second direction on the controlling plane 8). The angle made by the first and second directions, namely, the angle of twist of the liquid crystal molecules may be suitably selected, but usually such angle is defined to be about 90 as shown in Fig. 2.

A first polarizer 9 and a second polarizer 10 are disposed on the outside of the substrates 1 and 2, respectively. These two polarizers 9, 10 are usually arranged such that the angle made by their respective axes of polarization will be equal to the twist angle of the liquid crystal molecules (the angle made by said first and second orientation directions) or will be zero (in this case the respective axies of polarization are parallel to each other), and that the axis of polarization of each polarizer will be parallel to or cross at right angles with the liquid crystal orienting plane of the associated substrate.

Such display element is widely utilized as a reflection type display element by providing a reflector 11 on the back side of the second polarizer 9 for effectuating normal display as seen from the first substrate side, or as a night-time display element by further incorporating a photoconductor made of an acrylic resin, glass or the like with a suitable thickness between the second polarizer 9 and reflector 11 and placing a light source on a suitable location on a side of said photoconductor.

Here, the operational principle of a reflection type liquid crystal display element arranged with 900 twist angle and 900 polarization axes crossing angle is described.

In case no electric field is present in the liquid crystal layer, the incoming light (ambient light incident upon the first polarizer 9 of the liquid crystal display element) is transmitted through the first polarizer 9 to become rectilinear polarized light running along the axis of polarization and enters the liquid crystal layer, but since the liquid crystal molecules are twisted 900 in said layer, the plane of polarization of the polarized light is optically rotated by 900 upon passage of the light through the liquid crystal layer, and then the polarized light passes the second polarizer 10. This polarized light is then reflected on the reflector 11 and transmitted reversely through the second polarizer 10, liquid crystal layer 4 and first polarizer 9 in that order and finally emanated out of the liquid crystal display element.Thus, the observer can see the polarized light which has entered the liquid crystal display element and again comes out of said element after reflected by the reflector.

On the other hand, when a predetermined voltage is applied to a certain selected electrode 6 to give an electric field in a certain area of the liquid crystal layer in said display element, the liquid crystal molecules in that area are oriented in the direction of the electric field, and as a result, such area of the liquid crystal layer is deprived of its optical rotating capacity for the polarization plane and hence the plane of polarization in said area undergoes no optical rotation, so that the light polarized by the first polarizer 9 is intercepted by the second polarizer 10 and therefore that area looks dark to the observer.

It is thus possible to effect desired display by applying an electric voltage to a pertinent electrode.

In this invention, the transition temperature of a solid t,a a liquid crystal (or a smectic liquid crystal tt a nernatic liquid crystal) is decided and defined according to the results of the following measurements. There are many occasions where the individual single liquid crystal compounds or mixed compositions thereof undergo over-cooling.In such a case, the compound (or composition) is cooled to a sufficiently low temperature (for example 400 C) and then the transition temperature in the rising trend of temperature is measured by a micro melting-point measuring apparatus, and the thus measured temperature is given as transition temperature of the solid cut liquid crystal compounds (or the smectic liquid crystal o the nematic liquid crystal). This second requirement is of great significance not only for ordinary static driving but also for driving by a so-called multiplexing drive system.The multiplexing drive system according to, for example, the voltage-averaging method is now predominantly employed in the liquid crystal display devices, particularly those requiring voluminous informations, such as for example table-type electronic computers or matrix displays. Low voltage driving is desirable for the table-type electronic computers or the like, and usually there is employed a 4.5 V driving system (using three 1.5 V cells) or 3 V driving system (using two 1.5 V cells) where the cells are connected in series to effect direct driving. This low voltage driving requires no boosting circuit since the cells are connected in series, and also the cell life can be prolonged to 500 to 2,000 hours by combination with C-MOS.

However, such multiplexing drive system is subject, in principle, to certain operational restrictions which are not seen in the static driving system. In the multiplexing drive display devices, it is required to prevent cross-talks in the picture element at each half-selection or non-selection point, and the voltageaveraging method is most popularly used for prevention of such cross-talks. This method was deviced for expanding the operational margin by averaging the cross-talk voltages to enlarge the difference from the selection voltage. This method is explained below by citing a typical case of application.

Described here is a case of application of the voltage-averaging method where the cross-talk voltages are averaged down to 1/3 of the selection voltage and the driving wave form is made alternating. The driving wave form of this system is shown in Fig. 3 in which Vx is selection voltage, Vy is signal voltage, and Vx-Vy is applied voltage. In Fig. 3, a voltage of +Vo is applied to the liquid crystal in the selected condition while a voltage of +(1/3)Vo is applied to the liquid crystal in the half-selected or non-selected condition.In this case, the effective voltage v5 applied to the display point (the point at which the liquid crystal is brought into a displaying condition) is given by the following formula:

wherein N: duty number On the other hand, effective voltage 1'52 applied to the non-display point is given by: Vs2=1/3 Vo (2) Here, in order to evolve a displaying mode at the display point, effective voltage l 5, must be greater than or equal to threshold voltage Vth of the liquid crysta (#si#Vth), and in order to prevent cross-talks from being produced at the non-display point, effective voltage v52 must be smaller than or equal to Vth (1's2 < Vth).In other words, the following condition must be met for providing a cross-talk-free display according to this driving system: vs2#Vth#vs1 (3) Introducing the formulae (1) and (2) into the formula (3), Vo is defined as follows:

Measuring brightness at the display and non-display points by varying Vo, there are obtained the results such as shown in Fig. 4. At the display and non-display points exist the liquid crystal threshold voltages Vth1 and Vth2 as converted to the Vo basis, and when the following condition is met: Vth1#Vo#Vth2 (5) cross-talk-free display is made possible.From the formula (4), Vth, and Vth2 can be given as follows:

To be more exact concerning the formula (5), the lower threshold value of voltage that allows display is not Vth, but should rather be the saturation voltage Vsat, shown in Fig. 4. In other words, the voltage range that allows cross-talk-free display is given by the following formula: Vsat#Vo#Vth2 (8) It may be said that the greater the range of fluctuation of Vo in the above-formula (8), the broader is the operational margin (M) of the display device.In the above described derivation of formulae, vsl and 1'52 and hence Vth1, Vth2, and Vsat, are all considered as constant, but these values are actually variable depending on the ambient temperature (T), viewing angles to the element (#.) and other factors (Fig.

5). In the above explanations for the formula (1) through formula (8), viewing angle 0 defined in Fig. 5 is supposed to be 0, but actually such viewing angle may take a value within a limited range.

As viewed above, there are various factors that decide the operational margin (M). These factors are explained in due order hereinbelow, but it will be convenient for understanding such factors and the essence of the problem to give particular considerations to the following three essential elements: (i) variation of threshold voltage with change of temperature (ii) variation of threshold voltage with change of angle (iii) sharpness of voltage-brightness characteristic. The relation between (i) - (iii) and operational margin (M) will be clarified quantitatively by means of actual measurements.

The electro-optical characteristics of the multiplexing drive system are determined by the method illustrated in Fig. 6. A liquid crystal display element 51 is placed in a constant-temperature tank 53 with an inclination between 100 and 400 to the luminometer 52, and the brightness of said element 51 through a heat-absorbing glass filter 55 from a tungsten lamp 54 disposed with an angle of 300 to the luminometer 52, and the brightness of said element 51 is measured by the luminometer 52.

The driving wave forms in the case of 1/3 bias, 1/3 duty and 1/2 bias, 1/2 duty multiplexing drive as measured by the above-said method are as shown in Figs. and 8. Fig. 4 shows the voltagebrightness characteristics as determined from these wave forms. Fig. 4, region I is the area where the display is not lighted, and region II is the area where the display is lighted only at the selected segments.

Desired display of figures, letters, etc., can be made in the region II. Region Ill is the area where all the segments are lighted and no display function is performed, that is, cross-talk occurs. In the drawing, Vth, is voltage at selected segment (ON mode) of 10% brightness, Vth2 is voltage at non-selected segment (OFF mode) of 10% brightness, V5ati is 50% brightness selected segment voltage, and Vs,t2 is 50% brightness non-selected segment voltage.

The operational margin (M) is defined by the following formula:

wherein T = temperature ( C) 0-40 C # = viewing angle( ) 10-40 C f = frequency (Hz) 100-550 Hz Therefore, "broad operational margin" is synonymous with "broad region II". Thus, the multiplexing drive system must be driven in a certain range of voltage margin.

Further analysis of the operational margin (M) given by the formula (9) shows that M is decided by the afore-said three factors (i)-(iii), and these factors are quantitatively defined by the following formulae: (i) Temperature characteristic AT of Vth:

The definition is made under the following conditions:T = 0-40 C,# = 40 ,f = 100Hz. (ii)Angle dependency ##of Vth:

atT=400C,f= 100 Hz.

(iii) Sharpness y of voltage-brightness characteristic:

Although these three factors (i)-(iii) are the principal elements, usually frequency characteristic hf should be also taken into consideration as additional factor.

Af was defined under the conditions of T = 400C and 0 = 400 C.

The margin a of the voltage-averaging method is defined as follows for convenience of derivation of formulae: Vth2 &alpha; = (14) Vth1 Substituting the formulae (10)-(14) for the formula (9), operational margin Mis given as:

wherein

Generally, y, A0, AT and Af may be defined as follows: y > 1 AO < 1, AT > = 0 and Af < 1.

The hereabove defined operational margin may vary over a wide range depending on the liquid crystal compound used, but it is noticed that the compound capable of giving a greater margin is suited for multiplexing drive. As apparent from the formula (1 5), it is required for enlarging the operational margin M to make temperature characteristic AT approach zero as much as possible and to make the angle dependency AO, voltage-brightness sharpness and frequency characteristic Af approach as close to 1 as possible. In some cases, the effect of the temperature characteristic may be made almost ignorable in enlarging the operational margin by incorporating a temperature compensation circuit in the device.However, provision of such temperature compensation circuit necessarily leads to an elevated manufacturing cost of the device, so that it is desirable to employ the parts (elements) which can provide a wide operational margin with no extra condition such as provision of a compensation circuit, particularly in the case of the popularly used devices such as table-type electronic computers.

As for the third requirement, namely, good responsiveness over a wide temperature range, particularly at low temperatures, the following consideration will be instructive. Generally, responsiveness in the twisted nematic mode for multiplexing drive is given by the following formulae:

n: viscosity K: elastic constant (refer to formula (20) shown later) d: liquid crystal layer thickness It is noticed from the above formulae that liquid crystal responsiveness is decided mostly by viscosity of the liquid crystal material. It is said that these theoretical formulae well agree with actual measurements, and it is apparent to those skilled in the art that improvement of responsiveness can be attained by properly adjusting the viscosity of the liquid crystal compound used.

Thus, fulfillment of the third requirement depends on whether a liquid crystal compound having a low viscosity (and of course meeting the first and second requirements) can be found or not.

Concerning the three requirements which are to be solved in the development of liquid crystal materials for multiplexing drive, the present inventors have noticed the second and third requirements and examined relationship between physical constants such as viscosity, refractive index, dielectric anisotropy, elastic constant, etc., and display performance necessary for multiplexing drive such as the temperature dependency of threshold voltage (AT), the angle dependency of threshold voltage (by), the sharpness of voltage-brightness characteristic (y), the response properties, etc., for various liquid crystal materials as many as possible. As a result, the present inventors have found that liquid crystal materials can be divided into three groups; i.e. the first group contains liquid crystals having strong positive dielectric anisotropy represented by a symbol Nips, the second group contains liquid crystals having slightly weak positive dielectric anisotropy represented by a symbol NpW, and the third group contains a binary system of liquid crystals having negative dielectric anisotropy and positive dielectric anistropy represented by a symbol Nn + Np. Table 1 shows the symbols, the definitions, the examples as to the classification mentioned above.

TABLE 1

cu Definition Example "S, crystals having great ? o Np5 dielectrIc an isotropy flCmH2m+1 cH=NOcfl (AE 20) Np Liquid crystals having slightly weak positive NpW + anisotropy nCmH2m+iOOCN (A 10) C: crystals having negative -c Nn dielectric anisotropy flCmll 2m+10 CHNflq}l2q+1 (AE ck 0) Nn E crystals having remarkably weak Nn+ positive dielectric an Isotropy 03H70 OCOOOC5H11 5 zo c cn n < 0 0 < 0 0 < ,0 0 < 0 0 E D VE AR X c W < c su Y c u B0 otO - 0. - .O < CO Figure 9 is a diagram showing relationship between AT, which is an important display properties for multiplexing drive, and viscosity, which control response properties of liquid crystals, for various liquid crystals. As is clear from Figure 9, the binary system of Nn + Np types is superior to Np types such as NpW and Np" in properties for multiplexing drive. Further, it has been found by the present inventors that, in the binary system of Nn + Np types, the use of an Nn type cyclohexyl carboxylate such as

as the Nn type liquid crystal is better than the use of an ester of Schiff base type liquid crystal as the Nn type liquid crystal (e.g.Japanese Patent Application No. 150513/77). Still further, the present inventors have found that special combinations of special members selected from 4-substituted cyclohexane carboxylic acid-4'-substituted phenyl esters (hereinafter referred to as ECH) disclosed in East German Patent No. 105,701 and biphenyl type liquid crystals are effective for attaining the objects of this invention; Now explanations are given to individual components of the liquid crystal composition of this invention.

Examples of 4-substituted phenyl-trans-(equatorial-equatorial) cyclohexyl carboxylate of the formula (I) mentioned above are:

wherein m and q are each integer of 1 to 10, among them, the compounds having the following combinations of (m, q) being preferable: (2, 6), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 9), (4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6). (4, 8). (5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6). (5. 7), and (6, 3);

wherein m and q are each integer of 1 to 10, among them, the compounds having the following combinations of (m, q) being preferable:: (5, 1), (5, 2), (5, 3) and (5, 5);

wherein m and q are each integer of 1 to 10, among them, the compounds having the following combinations of (m, q) being preferable: (3, 4), (4, 2). (5. 2), (5, 3), (5, 9), and (6, 3);

wherein m and q are each integer of 1 to 10, among them, the compounds having the following combinations of (m, q) being preferable: (5, 3) and (5, 5).

In the mixed system of at least one compound of the formula (I) and at least one compound of the formula (II), it is desirable that individual compounds of the formula (I) and (II) have wide mesomorphic ranges (MR) so as to be a matrix system satisfying the requirements of the second and third ones mentioned above.

Table 2 shows mesomorphic ranges (MR) of major Nn type 4-n-alkyl-cyclohexane carboxylic acidtrans-4'-alkoxyphenyl esters.

TABLE 2

"-CmH2m+ I n~CmH2m+1{+ COO + O-n-cqH2q+ &num; Symbol n-CmH2m+ n-CqH2q+, MR (^C) A C2H5 C6HX3 22 - 45 B C3H7 CH3 56 - 63 C QH7 C2H5 47 - 79 D C3 H7 C3 H7 55 - 64 E C3H7 C4H5 42 - 73 F C3H7 CsH1, 37 - 67 G C4H9 CH3 42 - 59 H QH9 C2H5 36 - 76 l C,H, C3 H7 33 - 59 J C4 Hg C4H9 38 - 69 K C,H, Cs 29 - 66 L C4H9 C,H, 25 - 70 M C5H11 CH3 36 - 64 N CsH1i C2H5 55 - 86 O CsHll C3H7 38 - 66 P CsHll C4H9 49 - 81 Q CSHll CsHu 28 - 70 R C6H3 t H 50 - 66 When these compounds as listed in Table 2 are mixed, mixed systems having considerably wide MR as shown in Table 3 can be obtained.

TABLE 3

Mixed liquid crystal system: MR No. figure in parentheses shows % by mole ( C) Note 1-1 A(50) + B(50) 15-54 1-2 A(50) + C(50) 10-62 1-3 B(50) + D(50) 40-63 1-4 G(50) +H(50) 21-68 1-5 Q(50) + L(50) 13-70 16 J(50) + Q(25) + K(25) 9-69 1-7 K(50) +N(50) 12-76 1-8 Q(50) + N(50) 25-78 1-9 L(33.3) + N(33.3) + Q(33.3) 4-76 1-10 K(33.3) + N(33.3) + Q(33.3) 11-72 1-11 F(50) + Q(25) + L(25) 9-70 1-12 F(40) + N(20) + Q(40) 4-75 Mixed Liquid Crystals (1) 1-13 F(33.3) + Q(33.3) + L(33.3) 11-70 1-14 F(33.3) + K(33.3) + Q(33.3) 1569 1-15 F(33.3) + N(33.3) + N(33.3) 12-72 1-16 F(33.3) + N(33.3) + L(33.3) 1-17 K(33.3) + L(33.3) + N(33.3) 12-67 1-18 F(33.3) + H(33.3) + N(33.3) -3-72 Mixed Liquid Mixed Liquid Crystals (l) listed in Table 3 having a viscosity of about 23 centiposises (cp) at room temperature (25 C). On the contrary, known ester type liquid crystals having a benzenering in place of a cyclohexane ring in the molecular structure have a viscosity about 3 times as large as that of Mixed Liquid Crystals (I).

As the biphenyl series liquid crystals of the formula (II), those listed in Table 4 can preferably be used alone or as a mixture thereof. In general, biphenyl series liquid crystals of the formula:

wherein R3 is n-C,H2,+1 or n-C,Hz,+1-O; and r is an integer of 1 to 10, are preferably used as the compound of the formula (ll). TABLE 4

R 3ffThoo C-S1 N or I S-N N-I No. R3 y Temp. (0C) Temp. (0C) Temp. N c r F X cq t t t D 46.5 - (16.5) 4-2 n-C5H11 CN 22,5 - 35 4-3 n-C6H13 CN 13.5 - 27 Z tOU) UBU) X n-C8 I I CN t I I I 32.5 40 1S 4-7 n-C3H7 CN 71.5 - (64) 4-8 n-C4H9 CN 78 - (75.5) 4-9 n-C5H110 CN 48 - 67.5 4-10 n-C6H130 CN 58 - 76.5 4-Il n-C7H15 x CN 53.5 z X d t s 75 ss - E x ua uz u) D X t 1t 4-14 n-C6 H13 0 NO2 67 - (32.5) =t > Z Z Z Z Z Z Z Z Z Z Z Z O O O O C) Z Z Z Z 0000 000 eb 7 U b , O C OC OC CC) OC OC OC C O r C\l CO t U) D X 1 7 , , D} 8 < 7 ~ t Parentheses show a monotropic transition.

NOTE) C: crystal, N:nematic,c, S: smectic, 1: liquid Mesomorphic ranges (MR) of mixed systems of at least one compound of the formula (I) and a compound of the formula (II) are listed in Tables 5 and 6.

Table 5 shows mesomorphic ranges (MR) of mixed systems of Mixed Liquid Crystals (II) listed in Table 3 represented by the general formula:

which is Nn type liquid crystal, and one example of the No type biphenyl liquid crystals of the formula (II). that is.

hereinafter referred to as "BP-5".

TABLE 5

Mixed system Mixed Liquid Crystals (ll) BP-5 No. (% by wt.) (% by wt.) MR ( C) A-l 95 5 24 - 71 A-2 90 10 37 - 69 A-3 85 15 45 - 67 A-4 80 20 50 - 66 Table 6 shows mesomorphic ranges (MR) of mixed systems of Mixed Liquid Crystals (II) listed in Table 3 as mentioned above and one example of the Np type biphenyl liquid crystals of the formula (II), that is,

hereinafter referred to as "BP-05".

TABLE 6

Mixed system Mixed Liquid Crystals (ll) BP-05 No. (% by wt.) (% by wt.) MR ( C) B-1 95 5 29 - 74 B-2 90 10 44 - 75 B-3 85 15 56 - 75 B-4 80 20 62 - 76 As is clear from the results of Tables 5 and 6, the mesomorphic ranges of the mixed systems of at least one compound of the formula (l) and at least one compound of the formula (II) are relatively narrow from the viewpoint of practical use.

In order to improve such a disadvantage of the mixed system of the compounds of the formulas (I) and (ll) without lowering desirable properties of the mixed system of Nn + Np types, and more deslrably with increasing the properties for multiplexing drive, it is necessary to add a third component to the mixed system. On finding out suitable third components, the following point was taken into consideration.

Generally speaking, in the case of a binary system of Nn type and Np type liquid crystals, much more examples with worse mutual compatibility appear, when individual Nn and Np type liquid crystals become simpler. For example, compatibility of a binary system of Nn + Np types comprising multicomponent series of Nn type Schiff base of the formula:

and a mixture of Np type Schiff base liquid crystals of the formulae:

in molar ratio of 1:2, is insufficient, as shown in Figure 10. That is, when the weight ratio of the Nn type to Np type liquid crystals becomes about 1 :1, the melting point of the nematic liquid crystal is raised to about 00C.

As the third components, at least one compound of the formula (Ill), i.e.

wherein R5 is n-CmH2m+1'=O,n-CmHm2+1-CO,n-cmHm2+1-COO,or n-CmH2m+1-OCOO;R6 is n CqH2q+1, n-CqH2q+1-O,n-CqH2q+1-CO, n-CqH2q+1-COO or n-c@H@@+1-OCOO;m and a are each integer of 1 to 10, and/or at least one compound of the formula (IV), i.e.

wherein m is an integer of 1 to 10, are used in this invention in order to increase compatibility of the mixed system of Nn and Np type liquid crystals of the formulas (I) and (II).

Preferable examples of the compounds of the formula (III) are as follows:

wherein m and q are each integer of 1 to 6, and the combinations of (m, q) being (1, 4), (2, 4), (3, 4), (4, 1), (4, 6) and (5, 4) are more preferable among these compounds.

wherein m and q are each integer of 1 to 7, and the combinations of (m, q) being (1,4), (1, 5), (1, 6), (2,5), (5, 3), (5, 4) and (6, 3) are more preferable among these compounds.

wherein m and q are each integer of 1 to 7, and the combinations of (m, q) being (1, 2), (1, 3), (1, 4), (1,5), (2, 4), (3,2), (3,4), (4,2), (4, 5), (5,2), (5, 3), (6, 2), (6, 3), (6,4), (7,2) and (7, 3) are more preferable among these compounds.

wherein m and q are each integer of 1 to 6.

wherein m and q are each integer of 1 to 6.

Table 7 shows concrete examples of the compounds of the formula (III) with their MR.

Table 8 shows mesomorphic ranges of mixed liquid crystals within the scope of the formula (I) listed in Table 2 and Nn type liquid crystals of the formula (III) listed in Table 7.

TABLE 7

I R5COO--R6 No. R5 R6 MR ("C) R 7-1 CH3-O z z C4H9 40 - (43) 7-2 CH3-O C5H11 29 - 42 7-3 CH3-O C7H,s 34 - 43 7-4 C2H5-O CsHll 73 - (69) 7-5 03H7-O C5 H11 66 - (50) 76 C4H90 C5H11 68 - (63) 7-7 C5K11-D C3H7 41 - 49 7-8 C, H,,-O C8H13 40 - 47 7-9 C6H13-0 C3H7 56 - 59 7-10 C6H13O C4H9 50 - 53 7-11 CH13-O C5H11 50 - 63 7-12 CH3 OC4Hg 72 - (52) 7-13 C3H7 OC4Hg 72 - (59) 7-14 C4H9 OC6HI3 29 - (50) 7-15 CsH1l OC4Hg 49 - (58) 7-16 C6 -H 13 OC4Hg 39 - (49) 7-17 C6 H13 OCsH 41 - 44 7-18 CH3O OC4Hg 74 - 82 7-19 CH3O OC6H13 55 - 79 7-20 C2 Hs O OC4 H 9 94 - 105 7-21 C2H5O OC6HL2 83 - 98 7-22 C3H70 OCzH5 92 - 96 7-23 C3H70 OC4Hg 82 - 86 7-24 C4H ,O 0C2H5 97 - 101 7-25 C4HgO OC4Hg 86 - 91 Note) Values in parentheses mean monotropic transition. TABLE 8

No. Mixed system (% by weight) MR ( C) Note 2-1 No. 7-2 (33.3) + F(33.3) + Q(33.3) -4 - 63 2-2 No. 7-2 (30) + F(20) + N(20) + Q(30) -7 - 66 Mixed Liquid Crystals (lll) 2-3 No. 7-2 (33.3) + F(33.3) + N(33.3) 17 - 61 24 No. 7-2 (33.3) + B(33.3) + Q(33.3) 0 - 83 2-5 No. 7-2 (40) + F(40) + Q(20) 1 - 58 26 No. 7-2 (60) + F(20) + Q(20) 11 - 52 2-7 No. 7-2 (40)+N(20) + Q(40 -1 - 65 2-6 No. 7-2 (20) + N(40) +Q(40) 5 - 74 29 No. 7-2 (60) + F(20) + N(20) 18 - 55 2-10 No. 7-2 (33.3) +N(33.3) +Q(33.3) -1 - 68 Mixed Liquid Crystals (IV) 2-11 No. 78 (33.3) + F(33.3) + Q(33.3) 10 - 63 2-12 No. 7-8 (30) + F(20) + N(20) + Q(30) 15 - 68 2-13 No. 7-14 (33.3) + B(33.3) + Q(33.3) 5 - 55 2-14 No. 7-14 (60) + F(20) + Q(20) 3 - 54 2-15 No. 7-15 (60) + F(20) + Q(20) 15 - 56 2-16 No. 2-15 (20) + N(40) + Q(40) 11 - 65 2-17 No. 7-18 (33.3) + F(33.3) + N(33.3) 40 - 71 2-18 No. 7-18 (20) + N(40) +Q(40) 25 - 72 2-19 No. 7-19 (33.3) + F!33.3) + N(33.3) 28 - 70 2-20 No. 7-19 (20) + N(40) + Q(40) 20 - 73 Table 9 shows mesomorphic ranges of compositions comprising Nn type liquid crystals of the formula (I), a Np type liquid crystal of the formula (ll) (BP-5) and a third component of the formula (III), i.e.

TABLE 9

Composition Mixed Liquid Crystals (Ill) BP-5 No. (% by weight) (% by weight) MR ("C) C-1 95 5 -11 - 64 C-2 90 10 -40 - 62 C-3 85 15 -22 - 61 C-4 80 20 -4 - 59 C-5- 70 30 3 - 56 C8 60 40 7 - 54 Note) Mixed Liquid Crystals (Ill) (See Table 8).

20% by weight 30% by weight 20% by weight 30% by weight As is clearly shown in Table 9, the addition of the compound of the formula:

belonging to the compounds of the formula (III) in an amount of 30 to 20% by weight based on the total weight of the composition to the mixed systems of Nn type liquid crystals of the formula (I) and Np type liquid crystal of the formula (II) gives remarkably broadened mesoinorphic ranges (MR) compared with the results shown in Table 5.

rhe ester series materials represented by the formula (III) can generally be regarded as a mediating material and are liquid crystal materials having negative dielectric anisotropy or remarkably weak positive dielectric anisotropy and can be represented by NnM() or NnM(+). Therefore, the compositions listed in Table 9 can be regarded as three-component systems represented by Nn + NnM() + Np (V-i) or Nn + NnM(+) + Np (V-2) As the mediating materials, the-compounds of the formula:

wherein m is an integer of 1 to 10, can also be used in this invention alone or together with one or more compounds of the formula (III). A mixture of an Nn type cyclohexyl carboxylate of the formula (I) and an Np type trans-4-substituted-(4-cyanophenyl)-cyclohexane (hereinafter referred to as "PCH") of the formula (IV) can be useful as relatively good material for multiplexing drive because each compound can dissolve the other mutually.

Figure 11 is a phase diagram of a mixture of Mixed Liquid Crystals !1). which are Nn type cyclohexyl carboxylate series liquid crystals, and Mixed Liquid Crystals PCH (I), the composition of which is shown in Table 10, belonging to trans-4-substituted-(4-cyanophenyl)cyclohexane series liquid crystals. As is clear from Figure 11, the Nn type cyclohexyl carboxylate series liquid crystals have good compatibility with the trans-4-substituted-(4-cyanophenyl)cyclohexane series liquid crystals and the mixed system has a broad mesomorphic range.

TABLE 10

Compounct % by wt. Note Compound % by wt. Note cIs 37 C3H7ffiO,/- CN 37 Mixed Liquid C5H11HOCN 36 Crystals PCH t I ) C7Hl5CN 27 Figure 12 is a phase diagram of a mixture comprising Mixed Liquid Crystals (I) shown in Table 3 belonging to the Nn type 4-n-alkylcyclohexane carboxylic acid-trans-4'-alkoxyphenyl esters of the formula (1-1)

belonging to the Np type biphenyl liquid crystals of the formula (11-1) and Mixed Liquid Crystals PCH (I) shown in Table 10, wherein the weight ratio of Mixed Liquid Crystals ( to Mixed Liquid Crystals PCH (I) is 1:1.Figure 12 clearly shows that the PCH series liquid crystals are mediating materials (represented by the symbol NpM) in the three-component system of Nn + NpM + Np, that is, the addition of PCH in an amount of 50 to 20% by weight based on the total weight of the liquid crystals gives a remarkably broaded mesomorphic range compared with the results shown in Table 5.

Figure 13 is phase diagram of a mixture wherein

is used in place of

in the mixture of Figure 12 as the biphenyl liquid crystal of the formula (11-1) (Np type). It is clearly shown in Figure 1 3 that the mesomorphic range is greatly broadened by the presence of NpM in an amount of 50 to 25% by weight based on the total weight of the liquid crystals compared with the results shown in Table 6.

It is effective to add one or more Nn type liquid crystals as fourth component to the liquid crystal composition of this invention so as to increase compatibility of the Nn type cyclohexyl carboxylates of the formula (I) with the Np type liquid crystals of the formula (II) and/or so as to broaden the mesomorphic range of the resulting liquid crystal compositions.

As the Nn type liquid crystals used as the fourth components, those having electric polarity in the molecule and negative dielectric anisotropy and homologues thereof are preferable for giving good properties as mentioned above, i.e., increased compatibility and broadened mesomorphic range of the mixture of liquid crystals. The term "homologues" include non-crystalline compounds within the scope of the general formulae as defined below.

Preferable examples of such Nn type liquid crystals and homologues thereof are as follows.

R7:n-CmH2m+1, or n-CmH2m+1-O.

R8:n-CqH2q+1, or n-CqH2q+1-O.

m, q: integer of 1 to 10 Examples:

m,q:integer of 1 to 10 r: integer of 1 to 3 s: integer of 1 to 3 Examples:

m, q: integer of 1 to 10

q: integer of 1 to 9 R: (CH3)2-CH-O, or (CH3)2-CH(CH2)2-O

m, q: integer of 1 to 10

m, q: integer of 1 to 10

m, q: integer of 1 to 10

m, q: integer of 1 to 10

m: integer of 1 to 10

m, q: integer of 1 to 10

m: integer of 1 to 10

m, q: integer of 1 to 10

R7:n-CmH2m+1-O, or n-CmH2m+1-COO R8:n-CqH2q+1, or n-CqH2q+1-O.

m, q: integer of 1 to 10 Examples:

R7:n-CmH2m+1, n-CmH2m+1-O, or n-CmH2m+1-CO, R8:n-CqH2q+1, n-CqH2q+1-O,n-CqH2q+1-CO, or n-CqH2q+1-COO m: integer of 1 to 18 q: integer of 1 to 10 Examples:

m: integer of 1 to 10

m: integer of 1 to 10 q: integer of 1 to 8

m: integer of 1 to 12 q: integer of 1 to 10

m, q: integer of 1 to 10

m: integer of 1 to 18 q: integer of 1 to 6

R7: n-CmH2m+i R8:n-CqH2q+1 m, q: integer of 3 to 8

R7:n-CmH2m+1-O R8: n-CqH2q+, m, q: integer of 1 to 10 Example:

These liquid crystals having negative dielectric anisotropy and homologues thereof may be used alone or as a mixture thereof in an amount of preferably 50% by mole or less, more preferably 5 to 30% by mole, based on the total weight of the liquid crystal composition.

In the next place, in the case of using these mixed crystal systems in twisted nematic field effect type liquid crystal display elements, it is necessary to give a suitable threshold voltage value to the mixed liquid crystal systems by adjusting the dielectric anisotropy of the mixed liquid crystal systems, i.e. the value of E1 - E1= AE.

It is very easy to give desired positive dielectric anisotropy to the mixed liquid crystal systems mentioned above. Since the mixed system of this invention, i.e. at least one 4-substituted-cyclohexane carboxylic acid-4'-substituted phenyl ester of the formula (I), at least one biphenyl series liquid crystal of the formula (II), and at least one mediating material of the formula (III) and/or (IV), is positive with a relatively small value, greater positive values of the mixed system can be obtained by adding a relatively small amount of one or more nematic liquid crystals having strongly positive dielectric anisotropy (Np type) or homologues thereof to the mixed system without changing greatly desirable good properties of the mixed system, such as a broad mesomorphic range, a low viscosity, and the like. That is, Np type liquid crystals mentioned below as the fourth component can be added to the liquid crystal composition of this invention alone or together with the Nn type liquid crystals mentioned above. The term "homologues" include non-crystalline compounds within the scope of the general formulae as defined below.

Preferable examples of such Np type liquid crystals and homologues thereof are as follows.

R4 n-CmH2m+g or n-CmH2m+1-O m: integer of 1 to 10 Examples:

R4: n-CmH2m+ or n-CmH2m+i-0 m: integer of 1 to 10 Examples:

R4 ll~CmH2m+1 m:integerof 1 to 10 Example:

R4:n-CmH2m+1, n-CmH2m+1-O, n-CmH2m+1-CO, or n-CmH2m+1-COO.

m: integer of 1 to 10 Examples:

R4:n-CmH2m+1 m: integer of 1 to 10 Example:

R4:n-CmH2m+1 m: integer of 1 to 10

R4:n-CmH2m+1 m: integer of 1 to 8

R4: n-CmH2m+1 m: integer of 1 to 8 X: F, Br, CI or I (halogen) Example:

R4:n-CmH2m+1 m: integer of 1 to 10

R4:N-CmH2m+1 m: integer of 1 to 8 X: F, CI, Br or I (halogen) Example:

R4:n-CmH2m+1 m; integer of 1 to 10 Example:

R4:n-CmH2m+1 m: integer of 1 to 10 When these Np type cpmpounds are added together singly or in admixture as voltage adjusting agent to the mixed system, the following general facts or rules may be the guiding principle for deciding the amount of the Np type liquid crystal to be added.That is, the amount of the Np type liquid crystal and/or its homologues to be mixed with the matrix Nn type liquid crystal is decided by the working threshold voltage required by the mixed system. The relation between the amount of the Np type compound to be mixed and working threshold voltage is determined substantially according to the following conceptions. The threshold voltage (Vth) of the twisted nematic liquid crystal element is given by the following formula:

wherein # is twist angle which is usually :r/2, and K11, K22 and K33 are elastic constants of splay, twist and bend, respectively.The above formula (18) may be simplified as:

wherein AE = c11

It is possible, in principle, to obtain a liquid crystal with desired AE by mixing the liquid crystals with different values of Ac. Let it be assumed here that dielectric constants of the two different kinds of liquid crystals A and B are AEA and Ace, respectively, and the mixing ratio thereof is A/B = > /( 1 X), then if additivity of the dielectric constants applies here, AE of the mixed system is given by the following formula:

Also, if it is supposed that additivity applies for K, too, then K of the mixed liquid crystal is given by the following formula::

Introducing the formulae (21) and (22) into the formula (19),

The threshold voltage may be calculated in the following way by giving the definite figures to the respective constants.

Let it be assumed that hEB of the Nn type liquid crystal is -0.3, AEA of the Np type liquid crystal

is 25, KB is 4 x 1 G-7 dyne and KA is 17 X 10-17 dyne, then the formula (21) gives:

It will be apparent to those skilled in the art that above assignment of figures to AREA, åEB, KA and KB are not arbitrary but well conform to the actual properties of the liquid crystal.

Fig. 14 shows the relationship between the mixing ratio and the value of Vth (static drive) in case the Np and Nn type liquid crystals are mixed by using

as Np type liquid crystal and Mixed Liquid Crystal (III) shown in Table 8 as Nn type liquid crystal. The product of the theoretical formula (calculation formula) (23) or (24) well agrees with the experimental results.

More concretely, these liquid crystals having positive dielectric anisotropy and homologues thereof may be used alone or as a mixture thereof in an amount of preferably 2 to 50% by mole, more preferably 10 to 40% by mole, based on the total weight of the liquid crystal composition.

In addition, the following proportions in the composition are preferable: (a) at least one compound of the formula (i) 12 to 67% by weight, (b) at least one compound of the formula (Il) 5 to 55% by weight, (c) at least one compound of the formula (III) and/or at least one compound of the formula (IV) 5 to 40% by weight, and if required, (d) at least one nematic liquid crystal compound having positive dielectric anisotropy and/or its homologous compound 0 to 35% by weight and/or (e) at least one nematic liquid crystal compound having negative dielectric anisotropy and/or its homologous compound 5 to 20% by weight.

Generally speaking, there is a tendency to lower the nematic-to-isotropic transition temperature (N-I point) for liquid crystals by the addition of non-liquid crystal materials (liquid crystal homologous materials). For example, when a compound of the formula:

which is an Nn type liquid crystal homologue, is added, the N-I point of the patent liquid crystals is lowered. In many cases, the lowering of the N--l point accompanies deterioration of AT (increase of AT).

The increase of AT naturally relates to a decrease of M (the operational margin) as is clear from the equation (15). Effective materials (additives) for preventing the lowering of the N-I point, the increase of AT and, if possible, for increasing values of the operational margin (M) are listed in Tabel 11. The liquid crystals listed in Table 11 are those having relatively long molecular chains and are added in an amount of 2 to 30% by weight for increasing the N-I point of the resulting liquid crystal mixtures and for improving M (the operational margin).

TABLE 11

No. Long chain liquid crystal MR ("C) L-1 n-C 5Hll CN 131 - 238 L-2 3 - & fThOOCN 133 - 230 L-3 n-C 5H ll Cie 94 - 219 L4 n-C4Hg G CN 94 - 245 L-5 n-CIIH9-0CN 139 - 266 LZ n-C4HgX COOCOOCH9n 89 - 179 L-7 n-C4H9 &commat;cooe Coo0C2H5 138 - 225 LB n-C1H90 - COO COO--CqHg-n 112 - 212 L9 z 3 7 < COOwCN 121 - 236 L-1O n-C3H7 ------C00 C3H7-n 92 - 158 TABLE 11 (Continued)

No. Long chain liquid crystal MR ( C) 7 L-11 "-C3H7- -( iI wcoo+C3 7 n 0 2- COO -( 0 )C- C 3H7'" 87 - 186 L-12 n-CIlH944CO0+CN 112 - 235 L-13 n-C3H7 7 CIIH9-n 95 - 183 The liquid crystal compositions of the present invention containing as major components the compounds of the formulae (I) and (II) are particularly excellent in responsiveness as shown in the following Examples.

Figure 1 5 shows relationship between a viscosity and response time (rise time) of various liquid crystal systems. Measuring conditions are as follows: distance between the electrodes is 10 jum, applied voltage to each liquid crystal system is 1.5 times of the threshold voltage Vth of individual liquid crystals (0 = 00, 250C and 90% value). As is clear from Figure 1 5, the biphenyl series liquid crystals are excellent in responsiveness considering the absolute values of viscosity of these compounds compared with other liquid crystal systems and the most excellent in responsiveness among these liquid crystal systems except for the phenylcyclohexane series (PCH series).

Various studies have also made on the introduction of excellent properties of responsiveness of the biphenyl series liquid crystals belonging to the NpW type to the binary system of Nn + Np types.

Figure 16 shows relationship between a viscosity and response time of binary systems comprising a biphenyl (NpW) and an Nn type cyclohexyl carboxylate liquid crystal of the formula (1-1). As is clear from Figure 16, these binary systems are also excellent in responsiveness considering the absolute values of viscosity as in the case of the biphenyl series.

The following Examples show the effect of addition of biphenyls on the improvement of responsiveness.

TABLE 12

c Angle Temp. *2 * 1 Central dependency dependency Response Example Margin voltage of Vth of Vth time No. E ~ (%) (V) (A0) (AT) (mins) An oX1 E n > I~ cq era I~ .o d ai (o + 7.5 s~ c: uz Example O baa .

- < > o 38 9 0.85 9.8 150 0.12 xo ~ O O O ~ w .cn &commat; H R x x x t.

:o trs N ts N w~ s C 9 9 9 + Z' Z' o + Z O O O 9 wS O o O O O N X o GD , > ~ , > cq Ul E a TABLE 12 (Continued)

Angle Temp. *2 *1 m dependency dependency u, d Margin voltage of Vth of Vth time No. Composition o; o weight) (V) (A0) (AT) (mins) An A < ~ E eo ot ~ ON a o' o o o o Er > F uz o o o | o C5H11CN (10) d z(10) s CD as 0.85 CD 140 0.13 o . . . .

O DC-- U) eD eD U) < =Qo cP, gDO- 2 C5H11CN' (20) ~ z(5) X (I, 0 > C00-CH9 (10) x(30) + Y(30) + ((IY 3 C5lI11CN (20) + z(ic) + 8.0 3.1 0.85 6.0 120 0.15 ô o O G u oE &verbar; ~ e &verbar; w Q Q &verbar; w zo o &verbar; x u ns Z E ~ E 111 E xX cG x xs O U] U1 Ul 111 TABLE 12 (Continued)

Angle Temp. *2 *1 Central dependency dependency Response Example Margin voltage of Vth of Vth tIme cn x(25) 8 Y(20) + r cn 4 C5H11CN(2o) + z(15) + 9.0 3.2 0.85 7.5 130 0.15 . > s 5 s oS .

,r d C5H11-CN(20) . z(15) c; o' o' X ! E N X X(30) + C3H7CN(25) + Ss- (c, + o 6 9.0 3.2 0.85 7.5 130 0.15 cllY ai a, + Z(15) + + ++ +In 3 o t ô g g o X X N ^ X o cI r-l X C) O X C)-Om X 0 > Oo0o t U) O E O E E LU TABLE 12 (Continued)

- ---- -- -- I < I E; dependency dependency Response Example Margin voltage of Vth of Vth time No. Composition (% by weight) (%) (V) (AO) (AT) (mins) An o o cUOEr cu cu oB . .. ~ E o > t- c ,c Example 7 8.5 3.1 0.85 8.0 120 0.16 r-" 5,dy + n tDe > St . .

s^ lo In oD oo .. ~ . . ~~ aY + Z(5) + r 8 . . .

. .NCN( 10) O ~ t4 o ~ q o 3 O + Z Z + + E o ( tzpz P tt aS X m X X X t 5 X O O o X O O O x Z X E ILI Uxj Ul TABLE 12 (Continued)

Angle Temp. *2 *1 o' dependency dependency In Example Margin voltage of Vth of Vth time No. Composition by weight) (%) 0s (A6) (AT) (mins) An v, 20 oS 511 (A) F o 9 C3H7C0O0C5H11:20 (95) s 8.5 0.90 o 160 0.13 O - -- .

nS^ $ oD ca . .

- < > u) 10 0) Bs II 75 co cd ci ... 11 C5ll11CN(20) + 0.84 9.0 120 0.15 f--7 o H H H O + H 8 N UE UE t A ~ Z O O O UE ~ [n O O ~ O n &verbar; 4 + 4 o oO oO H m 4 9 O0 X + Q O > Q Q X X =n Xx X en S Xo O O O O O < < : O O o aw ~ E z É t e TABLE 12 (Continued)

Angle Temp. '2 '1 Central dependency dependency Response ci Margin voltage of o d Composition d a, + Y(20) + Example 12 c5}i 1'1CN(2o) a Z(1O) 8.5 3.4 0.86 8.0 130 0.14 Y - ---- -- ---- - Q 4-~ 9 eD u) o Example 13 eD uo CD cnrr a, c; O ~ . - 10) ~ Z X o I I CH30C00C5H11: 33.3 + + , < me\ 8 ~ O O S Ue X I + O b O ~ e O O O g E ~ t t ~ t Q &commat;; o H H U H rS H H H o o Z = N = o = tn UE = < O C-) zS o C,) O O O O +, s CQ e t E z i Ul ui TABLE 12 (Continued)

F * Central dependency dependency F d Margin voltage of Vth of Vth time No. Composition o, by weight) (%) (V) (AO) (AT) (mins) An 13(30) + Y(30) + 0r. 15 C5H1jCN(20) É oN oN ON P)Y oS F'CI > L? L? L? ar , co co o, 0 s5-f- P > O co co a3 cu o C3H7mThHOCN(25) + U U~ cq v o, 00- X ce cs 0 > v 'n o, o. u) + Z X Ô 4 t t ss s t X o X v $ < Ô mI X X N :1: X wz ~ U) U w gLN UE a m o o sn o o ax o o o o uz es rs E o E ux] ux] iii Note: *1:1/3 bias 1/3 duty *2: 25 C, distance between the electrodes 10 m As shown in Table 12, the composition of Comparative Example 3 comprising the following liquid crystals: Nn (ECH) + NpW (PCH) + NpS (ester) + Long chain (diester) and designed to show central voltage of 3.1 V (1/3 bias, 1/3 duty) has the operational margin of 8.5% and the response time (rise time) of 1 60 mins.

On the contrary, the compositions of Examples 1 and 2 containing the biphenyl in an amount of 10% or 20% by weight, respectively, have response time reduced in 1 3% to 25% while lowering in the operational margin being as small as 0.5 to 1.5%. The compositions of Examples 3 to 8 containing 109/0 or 20% by weight of the biphenyl show excellent responsiveness, i.e. response time of 1 30 mins or less, as well as practically high operational margin of 8% or more. The compositions of Examples 11, 12, 13, 1 5 and 1 6 containing 20% by weight of the biphenyl have response time of 1 30 mins or less and operational margin of as high as 7 to 8.5%.

As is clear from Table 12, the liquid crystal compositions containing the materials of the formula (I) and the formula (II) as major components have faster responsiveness than that expected from the absolute values of viscosity. This is one of important advantages of the liquid crystal composition of the present invention.

Other excellent features relating mainly to optical properties of the composition of the present invention containing the materials of the formula (I) and the formula (II) are as shown below.

Refractive index anisotropy (An) of liquid crystal compositions is one of physical constants which have great influence on the liquid crystal display properties. The smaller An becomes, the larger viewing angle becomes. But, on the other hand, since optical rotational ability of the TN type liquid crystal display element is in proportion to An.d (wherein d is the thickness of the liquid crystal layer), when An is small in the case of thin liquid crystal layer, it is possible to cause so-called staining or coloring on the display surface due to passing of short wavelength light through the element without being rotated.

Therefore, it is desirable that the value of refractive index anisotropy of the liquid crystal composition is adjusted to meet the device conditions to be used.

The value of An of the liquid crystal materials of the formula (I) (Nn type), which is one major component of the liquid crystal composition of the present invention is about 0.1 to 0.12.

As the Np type liquid crystals, which may be used in a large amount in combination with the Nn type liquid crystalls, there may be used PCH, NpW type liquid crystals, and the like, having An of about .0.1 1 to 0.13. Therefore it is impossible to control the value of An of the mixed liquid crystal composition in broader range in the combination of ECH (Nn) + PCH (Nn).

On the other hand, since the biphenyl type liquid crystals (NpW type) have An of about 0.22 which is great next to Schiff base liquid crystals, it becomes possible to adjust the value of An in a broader range of 0.10 to 0.22 if a binary system of Nn (ECH) + Np (biphenyl) is obtainable. This is because the addition rule can be applied to the proportions of individual components as to the value of An.

Figure 17 shows relationship between the composition of the binary system mentioned above and An. In Figure 17, MR (N-I point and C-N or S-N point) of the binary system is also drawn. That is, in the simple composition of Nn(ECH) + Npw (biphenyl), an increase of the content of one of the components makes the MR narrower. In order to remove such a defect mentioned above, the addition of the mediating material or materials of the formula (III), the ester type liquid crystals (Nn type), and/or of the formula (IV), PCH (NpW type), is effective for the liquid crystals of ECH (Nn type) and biphenyl type Npw type).Thus it is possible to obtain a practically useful liquid crystal composition excellent in multiplexing drive properties by mixing one or more ester type (Nn type) liquid crystals (An = 0.14) of the formula (III) and/or PCH (Np type) liquid crystals (An = 0.1) of the formula (IV).

Figure 1 8 shows relationship between An and the proportion of E-7 in mixed liquid crystal (I). As is clear from Figure 18, the presence of the ester type (Nn type) liquid crystal as the mediating material in an amount of 30% by weight make the MR broader.

The compositions of Examples 2, 3, 4, 6, 11, 12 and 1 5 comprise Nn (ECH) + NpW (PCH) + NpW (biphenyl) and have An of 0.14 to 0.1 5, these compositions being valuable for designing the elements optically.

Concerning An in relation to coloring, the standard for designing the elements is shown in Table 13.

TABLE 13 Relationship between thickness of liquid crystal layer and #n in relation to coloring.

(Viewing through the polarizing plate)

U (Ur0000000 ON .~~~ of liquid N 0.12 O O O O O O O . layer 4m 5 5 4 4 3 2 2 5 5 4 3 2 2 1 1 6 4 3 2 1 1 0 0 7 3 2 1 I 0 0 0 ~ . ~ 9 2 1 0 0 0 0 0 10 I 0 0 0 0 0 0 II el I 0 0 0 0 0 0 12 0 0 0 0 0 0 0 * t - - O O O O ~ U) O O O uo N N o ss X t W O s m o ~ Note) Evaluation of coloring: 0: transparent 1: slightly blue 2: pale blue

Usable as display elements 3: bluish violet 4: dark bluish violei 5: black

Difficult to use as display elements The three-component system of Nn (ECH + NpW (PECH + Npw (biphenyl), or Nn (ECH + (ester) + NpW (biphenyl) may turther contain at least one l?yrimidine series (#n = about 0.26) or ester series (#n = about 0.16) liquid crystal belonging to the group Nps as agent for adjusting threshold voltage and optical anisotropy within the scope of the present invention.

The compositions of Examples 7, 8, 16 and 17 contain one or more pyrimidines and have An of as large as 0.16 to 0.18.

As to the first requirement for liquid crystal materials, i.e. good adaptability to the orientation controlling film, which is very important for practical use, the present inventors have studied in detail with many experiments of orientation of the compounds of the formula (I) and biphenyl series liquid crystals, which are main components of the present invention. As a result, these compositions had good orientation properties for SiO oblique vacuum metalized films, rubbed organic polymer films, rubbed carbon films, and the like.

The liquid crystal composition of the present invention may further contain a small amount of one or more additives as a fifth component in order to show desirable properties, e.g. prevention or removal of domain due to the rotational properties. As the fifth components, there can be used cholesteric liquid crystals such as cholesteric chloride, cholesteryl nonanoate, etc., optically active materials such as 1menthol, 4'-(2"-methylbutyloxy)-4-cyano-biphenyl, etc.

It is also possible to form so-called phase transition type compositions by adding an increased amount of these materials giving optical activity to the compositions of the present invention.

The compositions of the present invention can also be applied to the color display effect called as "guest-host" or "phase change with dye" with the addition of multicolor dyes. Further, the compositionsof the present invention are also useful as liquid crystal materials for field effect types such as those applying changes of double refraction of liquid crystals by electric field.

As is clear from the above explanations, the liquid crystal compositions of the present invention are preferable for display devices, since they are white. Further, since the compositions of the present invention are strongly resistant to light and chemically stable, they have high reliability as liquid crystal mater ials. At the same time, since the compositions of the present invention are more excellent in responsiveness, have a broader margin and better optical properties of hardly causing coloring compared with conventional liquid crystal materials for time-sharing driving, they are most suitable for use in liquid crystal display devices.

Claims (27)

1. A nematic liquid crystal composition for use in display devices comprising (a) at least one compound of the formula:

wherein R, is n-Cm H2m+1, n-CmH2m+,-O, or n-Cm H 2m+i -CO; R2isn-CqH2q+1, n-CqH2q+,-O or n-CqH2q+l-CO; m and q are each integer of 1 to 10; and n is a symbol indicating that the carbon chain is straight, (b) at least one compound of the formula:

wherein R3 is n-CrH2r+, n-C,H2r+1-O or n-CrH2r+,-COO; Y is CN or NO2; r is an integer of 1 to 1 0; and n is as defined above, (c) at least one compound of the formula:

wherein R5 is n-CmH2m+1, n-CmH2m+1-O, n-CmH2m+,-CO, n-CmH2m+,-COO or n-CrH2m+,-OCOO; R6 is n CqH2q+1, n-CqH2q=1-O, n-CqH2q+1-COO or n-CqH2q+1-OCOO; m and q are each lnteger of 1 to 10, and n is as defined above, and/or at least one compound of the formula:

wherein m is an integer of 1 to 10.

2. A nematic liquid crystal composition according to Claim 1, which further comprises (d) at least one nematic liquid crystal compound having positive dielectric anisotropy and/or its homologous compound, and/or (e) at least one nematic liquid crystal compound having negative dielectric anisotropy and/or its homologous compound.

3. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 n-CmH2m+1 or n-CmH2m+1-O; and m is an integer of 1 to 10.

4.A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+, or n-CmH2m+,-O; and m is an integer of 1 to 10.

5. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+; and m is an integer of 1 to 10.

6. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+1,n-CmH2m+1-O, n-CmH2m+1-CO or n-CmH2m+1-COO; and m is an integer of 1 to 10.

7. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-Cm H2m+i; and dmis an integer of 1 two 10.

8. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+,; and m is an integer of 1 to 10.

9. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+,; and m is an integer of 1 to 8.

10. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+,; m is an integer of 1 to 8; and X is halogen.

11. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+,; and m is an integer of 1 to 10.

12. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+l; m is an integer of 1 to 8; and X is halogen.

13. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m,1; and m is an imteger of 9 to 10.

14. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is a compound of the formula:

wherein R4 is n-CmH2m+1; and m is an integer of 1 to 10.

- 3 5. A nematic liquid crystal composition according to any one of Claims 2-14 wherein the component (e) is a compound of the formula:

wherein R7 is n-CmH2m+1 or n-CmH2m+1-O; R8 is n-CqH2q+1, or n-CqH2q+1-O; and m and q are each integer of 1 to 10.

1 6. A nematic liquid crystal composition according to any one of Claims 2-14, wherein the component (e) is a compound of the formula:

wherein R7 is n-CmH2m+1, n-CmH2m+1-O, n-CmH2m+1-COO, n-C.H2m+1-O-(CH@)@-O(CH@)@-CH-@@@ (CH3)2-CH(CH2)2-O;F R8 is n-CqH2q+1, @ n-CqH2q+,-O, n-CqH2q+,-CO, n-CqH2q+,-COO, n-CqH2q+,-OCOO,

m and q are each integer of 1 to 10; r is an integer of 1-to 3; and s is an integer of 1 to 3.

17. A nematic liquid crystal composition according to any one of Claims 2-14, wherein the component (e) is a compound of the formula:

wherein R7 is n-CmH2m+1-O or n-CmH2m+r-COO; Ra is n-CqH2q+1 or n-CqH2q+1-O; and m and q are each inteyer of 1 to 10.

18. A nematic liquid crystal composition according to any one of Claims 2-14, wherein the component (e) is a compound of the formula:

wherein R7 is n-CmH2m=1, n-CmH2m+1-O or n-CmH2m+10CO; R8 is n-CqH2q+1, n-CqH2q+1-O,n-CqH2Q+1-CO or n-CqH2q+1-COO; m is an integer of 1 to 18; and q is an integer of 1 to 10.

19. A nematic liquid crystal composition according to any one of Claims 2-14, wherein the component (e) is a compound of the formula:

wherein R7 is n-CmH2m+,; R8 is n-CqH2q+,; and m and q are each integer of 3 to 8.

20. A nematic liquid crystal composition according to any one of Claims 2-14, wherein the component (e) is a compound of the formula:

wherein R7 is n-CmH2m+,-O; R8 is n-CqH2q+1; m and q are each integer of 1 to 10.

21. A nematic liquid crystal composition according to any one of Claims 2-14, wherein the component (e) is a compound of the formula:

wherein R7 is n-CmH2m+1, or n-CmH2m+,-O; R8 is n-CqH2q+1, or n CiqH2q+1-O; m and q are each integer of 1 to 10.

22. A nematic liquid crystal composition according to CJaim 2, wherein the compound (d) is a compound of the formula:

wherein R4 is n-CmH2m+,; and m is an integer of 1 to 10.

23. A nematic liquid crystal composition according to Claim 2, wherein the component (d) is selected from the group consisting of

wherein R4 is n-CmH2m+1 or n-CmH2m+1-O; and m is an integer of 1 to 10,

wherein R4 is n-CmH2m+1 or n-CmH2m+,-O; and m is an integer of 1 tX 10,

wherein R4 is n-CmH2m+,; and m is an integer of 1 to 10,

wherein R4 is n-CmH2m+1, n-CmH2m+1-O, n-CmH2m+1-CO or n-CmH2m+1-COO; and m is an integer of 1 to 10,

wherein R4 is n-CmH2m+1; and m is an integer of 1 to 10.

wherein R4 is n-CmH2m+,; and m is an integer of 1 two 10,

wherein R4 is n-CmH2m+1; and m is an integer of 1 to 8,

wherein Ra is n-CmH2m+1; m is an integer of 1 to 8; and X is halogen,

wherein R4 is n-CmH2m+1; and m is an integer of 1 to 10,

wherein R4 is n-CmH2m+1; m is an integer of 1 to 8; and X is halogen,

wherein R4 is n-CmH2m+X; and m is an integer of 1 to 10, and

wherein R4 is n-CmH2m+1; and m s an integer of 1 to 10, and the component (ei is selected from the group consisting of

wherein R7 is n-CmH2m+1 or n-CmH2m+1-O;R8 is n-CqH2q+1, or n-CqjH2q+1-O; and m and q are each lnteger of 1 to 10,

wherein R7 is n-CmH2m+1, n-CmH2m+1-O,n-CmH2m+1-COO, n-C@H2@+1-O-(CH2))3-O, (CH3)2-CH-O or (CH3)2-CH(CH2)2-P;R8 is n-cqH2q+1, n-CqH2q+1-O, n-CqH2q+1-CO, n-CqH2q+1-COO, n-CqH2q+1-OCOO,

or

m and q are each integer of 1 to 10; r is an integer of 1 to 3; and s is an integer of 1 to 3,

wherein R7 is n-CmH2m+1-O or n-CmH2m+1-COO;R8 is n-CqH2q=1 of n-CqH2q+1-O; and m and q are each integer of 1 to 10,

wherein R, is n-CmH2m+I, n-CmH2m+1-O or n-CmH2m+1-CO;R6 is n-CqH2q+1, n-CqH2q+1-O n-CqH2q+1-CO or n-CqH2q+1-COO; m is an integer of 1 to 18; and q is an integer of 1 to 10,

wherein R7 is n-CmH2m+1, R8 is n-CqH2q+g; and m and q are each integer of 3 to 8,

wherein R7 is n-CmH2m+1, or n-CmH2m+1-O; Re is n-CqH2q+1, or n-CqH2q+1-O; m and q are each integer of 1 to 10, and

wherein R7 is n-CmH2m+1-O; Re is n-CqH2q+,; m and q are each integer of 1 to 10.

24. A nematic liquid crystal composition according to any one of the preceding Claims, wherein the proportions of the components (a), (b) and (c) are: (a) 12 to 67% by weight (b) 5 to 55% by weight (c) 5 to 40% by weight

25. A nematic liquid crystal composition according to any one of Claims 2-24, wherein the proportions of the components (a), (b), (c), (d) and (e) are: (a) 12 to 67% by weight (b) 5 to 55% by weight (c) 5 to 40% by weight (d) O to 35% by weight (e) 5 to 20% by weight.

26. A nematic liquid crystal composition according to claim 1 substantially as hereinbefore described with reference to any one of the Examples.

27. A liquid crystal display device using at least one liquid crystal composition according to-any one of the preceding claims.