JPH0785142B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device, and particularly to a twist nematic type (hereinafter, also referred to as “TN type”) suitable for a multiplex drive system (time division drive system). ) Related to the liquid crystal display device.

[Background of technology]

The liquid crystal display device has advantages such as low power consumption, low manufacturing cost, light weight and thinness, and easy colorization.
Applications are expanding, centering on types.

A TN type liquid crystal display device is constructed by enclosing nematic liquid crystal having a positive dielectric anisotropy between two alignment-treated electrode substrates, and usually the liquid crystal molecules are twisted by 90 ° continuously. It is said that.

This type of liquid crystal display device having a twist angle of 90 ° (hereinafter, also referred to as “90 ° twist type”) has advantages that it is easy to produce, suitable for mass production, and has a quick response.

However, this 90 ° twisted type liquid crystal display device transmits light (or reflected light) in response to changes in applied voltage.
Since the change in the intensity of the image is gradual, it is difficult to obtain a clear image with low contrast and the viewing angle is narrow when increasing the time division order during multiplex driving. There are limitations to applying the high multiplex drive method. For example, in a liquid crystal display device in which the size of the display screen is about A size, the duty ratio in multiplex drive is 1/20.
It is said that 0 or more is practically preferable, but in a practical liquid crystal display device, the duty ratio is about 1/100, and the contrast ratio (luminance ratio at the time of selection and non-selection) ) Is as low as about 3.

As a technique for solving the problem of such a 90 ° twist type liquid crystal display device, in JP-A-60-107020, a twist angle of liquid crystal molecules is 180 to 360 ° and at least one electrode substrate is used. A liquid crystal display device is disclosed in which the angle formed by the director direction of aligned liquid crystal molecules and the electrode substrate surface (hereinafter, also referred to as “pretilt angle”) is larger than 5 °. According to this liquid crystal display device, the intensity of the transmitted light changes sharply with respect to the applied voltage.
For example, when performing multiplex driving with a duty ratio of 1/100, it is said that a high contrast ratio of 19.6 can be realized.

However, in this liquid crystal display device, sufficient consideration has not been given to the bistable effect, and therefore, there is a problem that the response is slow when the liquid crystal display device is multiplex driven at a high duty ratio. That is, in the liquid crystal cell of this liquid crystal display device, a so-called hysteresis phenomenon occurs in which the intensity change of transmitted light when the applied voltage rises and when the applied voltage falls is different. There are problems that the range is narrowed, or the on / off response time becomes long. Further, as a result of these, display defects are likely to occur due to slight nonuniformity of the liquid crystal cell thickness, temperature change, and the like. Therefore, it is necessary to suppress the bistable effect as much as possible.

[Problems to be Solved by the Invention] From the above, the present inventors have found that the twist angle of liquid crystal molecules in a liquid crystal composition disposed between a pair of substrates each having an alignment layer has a magnitude of 180 degrees. 0 ° or more and 360 ° or less, and between the spontaneous twist pitch P _S of the liquid crystal molecules and the regulated twist pitch P _C of the liquid crystal molecules when the alignment layer forcibly regulates the alignment of the liquid crystal molecules, 0 < We proposed a liquid crystal display device having a characteristic that the relational expression (P _C −P _S ) / P _C ≦ 0.3 holds (see Japanese Patent Application No. 60-267081).

According to such a liquid crystal display device, the bistable effect of the liquid crystal cell can be suppressed to some extent, and as a result, the margin of the drive voltage can be increased, and the contrast ratio and the response speed can be considerably improved. it can.

However, recently, development of a liquid crystal display device capable of responding in an even shorter time has been desired,
There has been a need to further improve the above techniques.

[Object of the Invention]

The present invention has been made based on the above circumstances, and an object thereof is to provide a sufficiently high contrast ratio even when a multiplex drive is performed at a high duty ratio, and an extremely short on / off time. And to provide a liquid crystal display device having excellent response characteristics.

[Means for solving problems]

The liquid crystal display device of the present invention is a liquid crystal display device in which a liquid crystal composition is arranged between a pair of substrates each having an alignment layer,
It is characterized in that the following conditions (a) to (d) are satisfied.

(A) The twist angle of liquid crystal molecules in the liquid crystal composition disposed between the pair of substrates is 200 to 300 °.

(B) The angle (pretilt angle) between the director direction of the liquid crystal molecules in contact with the surface of at least one of the alignment layers and the surface of the substrate having the alignment layer is 5 ° or more.

(C) The following relational expression is established between the spontaneous twist pitch P _S of the liquid crystal molecules and the regulated twist pitch P _C of the liquid crystal molecules when the alignment layer forcibly regulates the alignment of the liquid crystal molecules. .

0 <(P _C −P _S ) / P _C ≦ 0.3 (d) The following relational expression is established between the twist elastic constant k ₂₂ and the bend elastic constant k ₃₃ of the liquid crystal composition.

1.8 <k ₃₃ / k ₂₂ <2.5 Further, (e) the dielectric anisotropy Δε of the liquid crystal composition
And the ratio Δε of the dielectric constant ε _{⊥ in} the direction perpendicular to the long axis of the liquid crystal molecule.
The feature is that / ε _⊥ is 1.8 or more.

[Advantageous effects of the invention]

Since the liquid crystal display device of the present invention satisfies the above conditions (a) to (d), the bistable effect in the liquid crystal cell is suppressed to the necessary minimum, as will be understood from the description of the examples below. As a result, even in the case of multiplex driving with a high duty ratio, a sufficiently high contrast ratio can be obtained, and the time required for on / off is extremely short and excellent response characteristics are provided.

According to the present invention, the contrast ratio is actually 13 or more,
In addition, a liquid crystal display device having a response time of 150 msec or less can be obtained, and the performance is remarkably superior to the conventional device.

Furthermore, by adopting the preferable condition (e),
In the liquid crystal display device, high-multiplex driving can be sufficiently performed with a low drive voltage, and an inexpensive liquid crystal display device with low power consumption can be obtained.

[Specific configuration of the invention]

 Hereinafter, the present invention will be specifically described.

FIG. 1 is an explanatory view showing an exploded main part of a liquid crystal display device according to the present invention. In FIG. 1, 1 and 2 are substrates having an alignment layer (not shown), 9 and 10 are polarizing elements,
C is a liquid crystal layer.

In the present invention, the size of the twist angle α of the liquid crystal molecule (a) needs to be 200 to 300 °, preferably 240 to 290 °.

When the twist angle α is less than 200 °, the intensity change of the transmitted light with respect to the applied voltage becomes gradual, so that a sufficiently high contrast ratio cannot be obtained during high-order time division driving,
In addition, the viewing angle becomes narrow. On the other hand, when the twist angle α exceeds 300 °, the contrast ratio increases, but on the other hand,
The time required for turning off becomes long, the response characteristic deteriorates, and the dripping of the alignment of liquid crystal molecules easily occurs at the time of switching on / off, resulting in deterioration of display quality.

The twist angle α is defined by the direction of the alignment treatment for defining the alignment direction of the liquid crystal molecules on the substrates 1 and 2, the type and amount of the nematic liquid crystal forming the liquid crystal layer C or the optically active substance added to the nematic liquid crystal. can do.

In FIG. 1, the twist angle α indicates a counterclockwise twist in the traveling direction of incident light, but this does not define the present invention, and the twist direction may be clockwise. .

In the present invention, (b) the director direction of liquid crystal molecules in contact with the surface of at least one of the pair of alignment layers,
It is necessary that the angle (pretilt angle) with the surface of the substrate having the alignment layer is 5 ° or more, preferably 15 ° or more. The director direction means a direction in which the long axes of liquid crystal molecules are preferentially aligned.

When this pretilt angle is less than 5 ° on either side of the pair of alignment layers, the intensity change of the transmitted light with respect to the applied voltage does not become abrupt, and the alignment of the liquid crystal molecules is changed at the time of switching between on and off. Drooling is likely to occur, resulting in poor display quality.

In the present invention, (c) spontaneous twist pitch of liquid crystal molecules
The following relational expression needs to be established between P _S and the control twist pitch P _C of the liquid crystal molecules when the alignment layer forcibly controls the alignment of the liquid crystal molecules.

0 <(P _C −P _S ) / P _C ≦ 0.3 …… When the value of (P _C −P _S ) / P _C is 0 or less, the bistability effect becomes large in the liquid crystal cell, and as a result, Although the contrast ratio is high, the time required for turning on / off is long, but the response characteristic is deteriorated. On the other hand, this (P _C −
If the value of (P _S ) / P _C exceeds 0.3, the intensity change of the transmitted light with respect to the applied voltage becomes gradual, and it is not possible to obtain a sufficiently high contrast ratio. Drooling easily occurs and the display quality is degraded.

Here, the spontaneous twist pitch P _S means a pitch in a natural twist of liquid crystal molecules generated in a liquid crystal by adding an optical rotatory substance or the like to a normal nematic liquid crystal. Specifically, as shown in FIG. 2, substrates 1 and 2 each having alignment layers 6 and 7 formed on opposing surfaces of support plates 11 and 21 are arranged in a wedge shape to form a liquid crystal cell. The liquid crystal composition is enclosed in this liquid crystal cell, and the spacing r between the stripes (disclination lines at every 1/2 pitch) and the liquid crystal cell thickness (liquid crystal C
It can be determined by the following formula by measuring the thickness d) and the liquid crystal cell length l.

Spontaneous twist pitch P _S = 2dr / l In FIG. 2, 8 is a spacer, 9 and 10 are polarizing elements, and the alignment layers 6 and 7 are subjected to alignment treatment in parallel directions.

Further, the regulated twist pitch P _C is calculated by the following formula in FIG. 1 by the thickness d of the liquid crystal layer C and the twist angle α of the liquid crystal molecules defined by the alignment treatment direction of the alignment layers of the substrates 1 and 2. Stipulated.

Regulating twist pitch P _C = (360 ° / α) × d In the present invention, the following relational expression is established between (d) the twist elastic constant k ₂₂ and the bend elastic constant k ₃₃ of the liquid crystal composition. It is necessary.

1.8 <k ₃₃ / k ₂₂ <2.5 ...... When the value of k ₃₃ / k ₂₂ is less than 1.8, the bistability effect is hardly obtained, and as a result, the intensity change of the transmitted light with respect to the applied voltage becomes gentle. , A sufficiently high contrast ratio cannot be obtained. On the other hand, when the value of k ₃₃ / k ₂₂ exceeds 2.5, the bistable effect becomes excessive, and as a result, the time required for turning on and off becomes long and the response characteristic deteriorates. Weeping is more likely to occur.

Since the liquid crystal display device of the present invention satisfies the conditions (a) to (d) as described above, even when the multiplex driving is performed at a high duty ratio, the intensity change of the transmitted light with respect to the applied voltage is further improved. In addition to being steep, a sufficiently high contrast ratio can be obtained, and the time required for on / off is extremely short and excellent response characteristics are provided.

Further, in the present invention, (e) the dielectric anisotropy Δε of the liquid crystal composition and the dielectric constant ε _{⊥ in the} direction perpendicular to the liquid crystal molecule major axis direction.
It is preferable that the ratio Δε / ε _⊥ of 1.8 is 1.8 or more. By selecting such a preferable range, it is possible to sufficiently perform high-multiplex driving with a low driving voltage in the liquid crystal display device, and it is possible to obtain an inexpensive liquid crystal display device with low power consumption.

If the value of Δε / _ε⊥ is too small, the driving voltage becomes high, and the intensity change of the transmitted light with respect to the applied voltage becomes gradual, which may make it difficult to obtain a sufficiently high contrast ratio.

Next, other preferable conditions for actually manufacturing the liquid crystal display device according to the present invention will be described.

(A) It is preferable that the liquid crystal composition is made of nematic liquid crystal, and the transition temperature T _NI from the nematic liquid crystal to the isotropic liquid of the liquid crystal composition is 90 ° C. or higher.

That is, by selecting such a preferable condition, it becomes possible to suppress a variation caused by a temperature change such as a display color, a driving voltage, and a response speed in a normal operating temperature range of the liquid crystal display device, As a result, a highly reliable liquid crystal display device can be obtained.

(B) The refractive index anisotropy Δn of the liquid crystal composition is preferably 0.12 or more.

That is, by selecting such preferable conditions, it becomes possible to make the liquid crystal cell thin, and as a result, the time required for on / off is extremely short and the response characteristics are further excellent.

(C) The viscosity η of the liquid crystal composition at a temperature of 20 ° C. is preferably 30 cp or less.

That is, by selecting such a preferable condition, the fall time in the liquid crystal display device can be extremely shortened, and a more excellent response characteristic can be obtained.

Furthermore, in the present invention, the refractive index anisotropy Δ of the liquid crystal C
The product Δn · d of n and the thickness d (μm) of the liquid crystal layer C is 0.
It is preferably 4 to 1.5, and particularly preferably 0.8 to 1.2. By selecting such preferable conditions, a higher contrast ratio can be obtained and the display screen can be brightened.

In FIG. 1, β is the polarization axis direction of the polarizing element 9 and the director direction of the liquid crystal molecules in contact with the surface of the substrate 1, that is, the direction in which the molecular long axis of the liquid crystal molecules is preferentially aligned (however, the liquid crystal When the molecule has a non-zero pretilt angle with the substrate surface, the angle formed by the director direction of the molecule onto the substrate surface (hereinafter referred to as “shift angle”)
Also called. ) Is the shift angle between the polarization axis direction of the polarizing element 10 and the director direction of the liquid crystal molecules in contact with the surface of the substrate 2.

These deviation angles β and γ are preferably set such that the value of the sum β + γ thereof is within ± 20 ° with ± 90 ° or 0 ° as the center. Furthermore, it is preferable that the value of the deviation angle β is set to a value within a range of ± 15 ° around (360 ° -α) / 2. Thus, the deviation angles β and γ
By setting the value of to a preferable value, the light transmission state can be made brighter, and the light non-transmission state can be made darker, and as a result, the contrast can be further improved.

Furthermore, in the present invention, the thickness d of the liquid crystal layer C and the spontaneous twist pitch P _S are set in order to stabilize the twisted state of the liquid crystal molecules and prevent the arrangement portion of the liquid crystal molecules having different twist angles from occurring. It is preferable that the following relational expressions hold during the period.

(Α / 360) −0.25 <d / P _S <(α / 360) +0.30 Means for obtaining a substrate having an alignment layer that can be used in the present invention is not particularly limited, and various conventionally known methods can be used. The means of can be adopted. Specifically, for example, Si
Means for orienting the surface of the substrate by vapor-depositing a vapor deposition material such as O, MgO, and MgF ₂ from an oblique angle, for example, a film of a polymeric substance such as an imide-based, amide-based, polyvinyl alcohol-based, or phenoxy-based Is formed on the surface of the substrate, and the surface of this coating is rubbed with cotton cloth, vinylon cloth, tetron cloth, absorbent cotton, etc. to form a groove in a certain direction on the surface of the substrate, and the alignment treatment is performed by a rubbing method, or the surface of the substrate is treated with carbon. It is possible to use a means of applying a chromium acid complex, an organic silane compound, or the like, or coating by a plasma polymerization method, etc., and orienting liquid crystal molecules to the substrate by chemical adsorption, or other means.

Examples of the liquid crystal composition constituting the liquid crystal layer C that can be used in the present invention include the nematic liquid crystal as shown below, or a mixture thereof. However, it is not limited to these.

(1) Cyclohexycarboxylic acid ester compound represented by the following structural formula (However, X is R (alkyl group having 1 to 18 carbon atoms, the same applies below), OR, CN, Represents ) (2) Biphenyl compound represented by the following structural formula (However, X is R, OR, Represents ) (3) Phenylcyclohexane compound represented by the following structural formula (However, X is R, OR, CN, Represents ) (4) Pyrimidine compound represented by the following structural formula (However, X is R, CN, And Y represents R, OR and CN. ) (5) Azo-azoxy compound represented by the following structural formula (However, X is -N = N-, Represents ) (6) Benzoate compound represented by the following structural formula (However, X is R, RO, And Y is R, OR, CN, Represents ) (7) Tolan compound represented by the following structural formula (However, X and Y are F, R, OR, and Represents (8) An ethane compound represented by the following structural formula (However, X and Y are R, OR, and The liquid crystal composition used in the present invention may contain a smectic liquid crystal component, a cholesteric liquid crystal component or the like, if necessary.

The optical rotatory substance contained in the liquid crystal composition used in the present invention is generally called a chiral nematic liquid crystal, for example, an ester type, a biphenyl type, a phenylcyclohexane type having an optically active group represented by the following general formula as an end group. Alternatively, nematic liquid crystal such as azo can be used.

(However, R ₁ , R ₂ and R ₃ are each an alkyl group or a hydrogen atom, and R ₁ , R ₂ and R ₃ are different from each other.) Specifically, for example, a compound represented by the structural formula shown below. Can be used.

The optically active substance contained in the liquid crystal composition used in the present invention is preferably one which can sufficiently shorten the spontaneous twist pitch per unit addition amount to the nematic liquid crystal, and such a substance is preferable. By selecting it, the necessary addition amount of the optically active substance to the nematic liquid crystal can be suppressed to a small amount, preferably 1.5% by weight or less, and as a result, the nematic liquid crystal produced from the addition of the optically active substance isotropic. It is possible to minimize the decrease in the transition temperature T _NI to the ionic liquid and to reduce the temperature dependence of the spontaneous twist pitch. In addition, in the present invention, in order to further reduce the temperature dependence of the spontaneous twist pitch, a plurality of types of optically active substances having mutually opposite temperature change coefficients of the spontaneous twist pitch may be used in combination.

[Specific Example]

 Hereinafter, specific examples of the present invention will be described.

FIG. 3 is an explanatory sectional view showing an embodiment of the liquid crystal display device according to the present invention. In the liquid crystal display device of this example, two substrates 1 and 2 are arranged so as to face each other in a separated state, and the substrate 1 is configured by providing an electrode layer 4 and an alignment layer 6 on the inner surface of a support plate 11. And the substrate 2 is a support plate
The inner surface of 21 is provided with an electrode layer 5 and an alignment layer 7. Further, the space between the substrate 1 and the substrate 2 is sealed by the seal portion 3 to form a liquid crystal cell. Inside the liquid crystal cell, a plurality of spacers 8 are arranged separately from each other, and a liquid crystal composition is filled therein to form a liquid crystal layer C. A front polarization element 9 and a rear polarization element 10 are provided on the outer surfaces of the substrates 1 and 2, respectively. In the figure, reference numeral 13 is a reflector provided on the surface of the outer element of the rear polarization element 10. In addition, in the transmissive liquid crystal display device, the reflector 13 may not be used.

The material for the support plates 11 and 21 is soda glass, borosilicate glass, quartz glass, or other glass; uniaxially stretched polyethylene terephthalate, polyether sulfone, polyvinyl alcohol, or other plastic sheet; aluminum, stainless steel, or the like. And the like can be used.

The electrode layers 4 and 5 are, for example, a support plate 11 having a thickness of 1.1 mm.
And 21 spaced apart parallel to the surface of, for example, the thickness
The transparent electrodes E and E'composed of 1000 liters of ITO (tin and indium oxide), and the transparent electrode E'constituting one electrode layer 4 and the transparent electrode E'constituting the other electrode layer 5 are respectively The electrodes are arranged alternately at right angles to form a matrix-type display electrode structure composed of pixels of 0.3 mm × 0.3 mm, for example.

The alignment layers 6 and 7 are formed by an oblique vapor deposition method (vapor deposition angle: 7 ° with respect to the support plates 11 and 21, respectively) using, for example, SiO as a vapor deposition material. For example, the thickness is 500Å.
It is composed of a vapor deposition film of.

In addition, the substrate 1 and the substrate 2 may be further provided with a dielectric layer, an alkali ion migration preventing layer, an antireflection layer, a polarizing layer, a reflecting layer and the like, if necessary.

The front polarizing element 9 is composed of “F-1205DU” (manufactured by Nitto Denko Corporation), and its polarization axis direction is relative to the director direction of liquid crystal molecules in contact with the surface of the alignment layer 6.
It is arranged so as to have a deviation angle β of 35 °. Similarly, the rear polarizing element 10 and the reflector 13 are "F-3205M".
(Made by Nitto Denko Corporation)
The 10 polarization axis directions are arranged so as to have a shift angle γ of 55 ° with respect to the director direction of the liquid crystal molecules in contact with the surface of the alignment layer 7.

The spacer 8 is made of glass fiber “PF-60S” (manufactured by Nippon Electric Glass Co., Ltd.), and the seal portion 3 is a struct bond “XN-5A-C” (Mitsui Toatsu Chemicals, Inc.). Manufactured).

<Example 1> As a liquid crystal composition constituting the liquid crystal layer C, a nematic liquid crystal A was mixed with an optically active substance (chiral nematic liquid crystal) "S".
-811 "(manufactured by Merck & Co.) was added in an amount of 1.376% by weight (this will be referred to as" liquid crystal composition 1 "), and a liquid crystal display device having the same structure as that shown in FIG. 3 was produced.

The characteristics of the liquid crystal composition 1 are as follows.

Ratio of twist elastic constant k ₂₂ and bend elastic constant k ₃₃ k ₃₃ /
k ₂₂ = 2.3 Ratio of dielectric anisotropy Δε and dielectric constant ε _⊥ perpendicular to the long axis of liquid crystal molecules Δε / ε _⊥ = 2.4 Nematic liquid crystal to isotropic liquid transition temperature T _NI = 9
7.4 ° C. Refractive index anisotropy Δn = 0.15 Viscosity at temperature 20 ° C. η = 20 cp In a liquid crystal display device having the above configuration, the liquid crystal cell thickness (thickness d of liquid crystal layer C) is 6.0 μm, and the twist angle α of liquid crystal molecules is It is 270 ° counterclockwise from the front, the spontaneous twist pitch P _S is 7.6 μm, the regulated twist pitch P _C is 8.0 μm, and the pitch ratio (P _C −P _S ) / P _C is 0.05. In addition, the alignment layer 6
And the director direction of liquid crystal molecules in contact with the surfaces of 7 and 7,
Angle formed between the surfaces of substrates 1 and 2 (pretilt angle)
Are 35 ° each.

A test of driving this liquid crystal display device by a multiplex drive system showed that the bistable effect was small, a high contrast ratio was obtained, and the time required for on / off was extremely short and had excellent response characteristics. Yes,
In fact, high-order time-division driving with a duty ratio of 1/300 or more was possible.

Further, this liquid crystal display device was driven by a multiplex drive system at a duty ratio of 1/100, and the contrast ratio and the on / off display response time were calculated.
The contrast ratio in the visible light region of ~ 700 nm, that is, the ratio of the reflected light brightness in the selected state (dark) and the reflected light brightness in the non-selected state (bright) is as good as 1:15 or more. It is possible to obtain an excellent clear image of, and the on / off response time is as short as 150 msec or less,
It was confirmed that the display response characteristics were excellent.

<Example 2> In Example 1, as a liquid crystal composition constituting the liquid crystal layer C, 1.402% by weight of a nematic liquid crystal B was added an optically active substance (chiral nematic liquid crystal) "S-811" (manufactured by Merck & Co., Inc.). A liquid crystal display device was produced in the same manner as in Example 1 except that the glass fiber "PF-70S" was used as the constituent material of the spacer 8 instead of the one (this is referred to as "liquid crystal composition 2").

The characteristics of the liquid crystal composition 2 are as follows.

Ratio of twist elastic constant k ₂₂ and bend elastic constant k ₃₃ k ₃₃ /
k ₂₂ = 2.0 Ratio of dielectric anisotropy Δε and dielectric constant ε _⊥ perpendicular to the long axis of liquid crystal molecule Δε / ε _⊥ = 2.1 Nematic liquid crystal to isotropic liquid transition temperature T _NI = 9
1.0 ° C. Refractive index anisotropy Δn = 0.13 Viscosity at temperature 20 ° C. η = 20 cp In a liquid crystal display device having the above configuration, the liquid crystal cell thickness (thickness d of liquid crystal layer C) is 7.0 μm, and the twist angle α of liquid crystal molecules is It is 270 ° counterclockwise from the front, the spontaneous twist pitch P _S is 8.9 μm, the regulated twist pitch P _C is 9.3 μm, and these pitch ratios (P _C −P _S ) / P _C are 0.05. In addition, the alignment layer 6
And the director direction of liquid crystal molecules in contact with the surfaces of 7 and 7,
Angle formed between the surfaces of substrates 1 and 2 (pretilt angle)
Are respectively 38 °.

A test of driving this liquid crystal display device by a multiplex drive system showed that the bistable effect was small, a high contrast ratio was obtained, and the time required for on / off was extremely short and had excellent response characteristics. Yes,
In fact, high-order time-division driving with a duty ratio of 1/300 or more was possible.

Further, this liquid crystal display device was driven by a multiplex drive system at a duty ratio of 1/100, and the contrast ratio and the on / off display response time were obtained in the same manner as in Example 1. The contrast ratio was 1:13 or more. It was confirmed that a clear image with excellent contrast was obtained, the on / off response time was as short as 140 msec or less, and the display response characteristics were excellent.

Comparative Example 1 In Example 2, as a liquid crystal composition, a nematic liquid crystal “ZLI-2116-100” (manufactured by Merck Ltd.) and an optically active substance (chiral nematic liquid crystal) “S-811” (manufactured by Merck Ltd.) were used. A comparative liquid crystal display device was produced in the same manner as in Example 2 except that the amount added was 1.20% by weight (this is referred to as "comparative liquid crystal composition 1").

The characteristics of the comparative liquid crystal composition 1 are as follows.

Ratio of twist elastic constant k ₂₂ and bend elastic constant k ₃₃ k ₃₃ /
k ₂₂ = 2.7 Ratio of dielectric anisotropy Δε and dielectric constant ε _{⊥ in} the direction perpendicular to the long axis of liquid crystal molecule Δε / ε _⊥ = 1.12 Transition temperature from nematic liquid crystal to isotropic liquid T _NI = 9
5 ° C. Refractive index anisotropy Δn = 0.12 Viscosity at temperature 20 ° C. η = 19 cp In the comparative liquid crystal display device having the above configuration, the liquid crystal cell thickness (thickness d of the liquid crystal layer C) was 7.0 μm, and the twist angle of the liquid crystal molecules was α is 270 ° counterclockwise from the front, spontaneous twist pitch P _S is 8.6 μm, regulated twist pitch P _C is 9.3 μm,
The pitch ratio (P _C −P _S ) / P _{C of these} is 0.08. The angle (pretilt angle) between the director direction of the liquid crystal molecules in contact with the surfaces of the alignment layers 6 and 7 and the surfaces of the substrates 1 and 2 is 36 °, respectively.

When a test for driving this comparative liquid crystal display device by a multiplex driving device was performed, a high bistable effect and a high contrast ratio were obtained, but in the liquid crystal composition, the value of the elastic constant ratio k ₃₃ / k ₂₂ was set. Is too large, and the ratio Δε / ε _⊥ of the dielectric anisotropy Δε and the dielectric constant ε _⊥ is also small. Therefore, it takes a long time to turn on and off, and the response characteristics are low. It has been difficult to drive time-sharing with high order of 200 or more.

Further, this liquid crystal display device was driven by a multiplex drive system at a duty ratio of 1/100, and the contrast ratio and the on / off display response time were obtained in the same manner as in Example 1. The contrast ratio was 1:11. Although it was large, the on / off response time was as long as 200 msec, which was inferior to the liquid crystal display devices of Examples 1 and 2.

Comparative Example 2 1.395% by weight of a nematic liquid crystal "ZLI-3243" (manufactured by Merck & Co.) as a liquid crystal composition, and 1.395% by weight of an optically active substance (chiral nematic liquid crystal) "S-811" (manufactured by Merck). Comparative Liquid Crystal Composition 2 "was used, and a comparative liquid crystal display device was produced in the same manner as in Comparative Example 1.

The characteristics of the comparative liquid crystal composition 2 are as follows.

Ratio of twist elastic constant k ₂₂ and bend elastic constant k ₃₃ k ₃₃ /
k ₂₂ = 1.6 Ratio of dielectric anisotropy Δε and dielectric constant ε _⊥ perpendicular to the long axis of liquid crystal molecules Δε / ε _⊥ = 2.0 Nematic liquid crystal to isotropic liquid transition temperature T _NI = 6
5 ° C. Refractive index anisotropy Δn = 0.14 Viscosity at a temperature of 20 ° C. η = 36 cp In a comparative liquid crystal display device having the above configuration, the liquid crystal cell thickness (thickness d of liquid crystal layer C) was 7.0 μm, and the twist angle of liquid crystal molecules was α is 270 ° counterclockwise from the front, spontaneous twist pitch P _S is 8.9 μm, regulated twist pitch P _C is 9.3 μm,
The pitch ratio (P _C −P _S ) / P _C was 0.05. The angle (pretilt angle) between the director direction of the liquid crystal molecules in contact with the surfaces of the alignment layers 6 and 7 and the surface of the substrates 1 and 2 is 35 °.

When a test of driving this comparative liquid crystal display device by a multiplex drive device was performed, in the liquid crystal composition, the value of the elastic constant ratio k ₃₃ / k ₂₂ was too small, and therefore, the bistable effect did not occur, and therefore, The intensity change of the transmitted light with respect to the applied voltage became gradual, and a sufficiently high contrast ratio could not be obtained. Actually, when the contrast liquid crystal display device was driven by a multiplex drive system with a duty ratio of 1/100 and the contrast ratio was obtained, it was as small as 1: 6, and sufficient visibility was not obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an outline of the present invention, FIG. 2 is an explanatory view for identifying a spontaneous twist pitch P _S, and FIG. 3 is an explanatory sectional view showing an embodiment of the present invention. . 1,2 ... Substrate, 11,21 ... Support plate 3 ... Seal part, 4,5 ... Electrode layer 6,7 ... Alignment layer, C ... Liquid crystal layer 9 ... Front polarization element, 10 ... Rear polarizing element 13 ... Reflector

Claims (2)

[Claims] 1. A liquid crystal display device comprising a liquid crystal composition arranged between a pair of substrates each having an alignment layer, wherein the following conditions (a) to (d) are satisfied. (A) The twist angle of liquid crystal molecules in the liquid crystal composition disposed between the pair of substrates is 200 to 300 °. (B) The angle between the director direction of the liquid crystal molecules in contact with the surface of at least one of the alignment layers and the surface of the substrate having the alignment layer is 5 ° or more. (C) The following relational expression should be established between the spontaneous twist pitch P _S of the liquid crystal molecules and the regulated twist pitch P _C of the liquid crystal molecules when the alignment layer forcibly regulates the alignment of the liquid crystal molecules. . 0 <(P _C −P _S ) / P _C ≦ 0.3 (d) The following relational expression should be established between the twist elastic constant k ₂₂ and the bend elastic constant k ₃₃ of the liquid crystal composition. 1.8 <k ₃₃ / k ₂₂ <2.5 …… 2. The ratio Δε / ε _⊥ between the dielectric anisotropy Δε of the liquid crystal composition and the dielectric constant ε _{⊥ in} the direction perpendicular to the long axis of the liquid crystal molecule is 1.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is 8 or more.