JPH0561073A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display element having of quick response and wide viewing angle. CONSTITUTION:In the liquid crystal display element which is, at least, composed of a liquid crystal driving cell, at least, one double refraction layer, and a pair of polarizing layers arranged so as to hold the double refraction layer from the outside, the sum (DELTAnd) of the retardation values of the liquid crystal layer and the double refraction layer, when the liquid crystal layer of the liquid crystal driving cell is oriented nearly in parallel with a substrate, satisfies the following expression as a characteristic; DELTAnd=lambda(k<2>-(theta/180)2)<1/2> (1), where, lambdais the wavelength of light, and 0.45mum<lambda<0.65mum, theta (a unit is a degree), is the sum of the twist angles of the liquid crystal layer and the double refraction layer, and 15<theta<400, and k is the integer of 1<=k<=4, and k>theta/180. A liquid crystal display that an optical parameter is easily designed, the speed of the response is high, and the visual angle dependency of a contrast is reduced, can be executed, and the liquid crystal display element is used not only for a display for a liquid crystal TV set displaying a moving picture, but also the displays for all aims.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal device having a fast response speed and a wide viewing angle.

[0002]

2. Description of the Related Art Liquid crystal displays are occupying a major position in the display field in place of cathode ray tubes because of their features such as low voltage driving, light weight and low cost. However, liquid crystal displays generally have slow response speed, and have drawbacks such as a decrease in contrast and a change in color tone depending on the viewing angle (hereinafter referred to as viewing angle dependency), and it is desired to solve these problems. It was

In view of the viewing angle dependence, a method of utilizing substantially parallel alignment of liquid crystal molecules for dark display and utilizing substantially vertical alignment of substrates for bright display, for example, normally black mode of twisted nematic (TN) display However, it is believed to have advantages over the normally white mode of TN displays, for example, and vice versa. In the system in which the substantially parallel alignment state of the liquid crystal molecules on the substrate is used for dark display, the retardation value (product of birefringence and thickness, Δnd ' ) Is designed to be.

[0004]

[Equation 2]

In order to increase the response speed of the liquid crystal display element, it is generally sufficient to reduce the thickness of the liquid crystal layer, but the retardation value can be only a discrete value from the above equation, and the smaller the order k'in the above equation, It is not preferable to simply reduce the thickness of the driving liquid crystal layer because the light transmission during dark display (excluding light having a wavelength of 0.55 μm) increases and the contrast decreases. There is also a constraint that the twist angle θ cannot be set to a too large value in order to increase the response speed.

[0006]

The inventors of the present invention have found that even if the optical parameters of the liquid crystal driving cell cannot be used for display as they are, the parameters can be improved by adding another birefringent layer having a twist structure. As a result of diligent study, it was possible to arbitrarily set the retardation and twist angle of the liquid crystal driving cell, the response speed was fast, the contrast was high, and the viewing angle dependence was small in the present invention. The device was found, and the present invention was finally reached.

That is, according to the present invention, a liquid crystal layer sandwiched between a pair of substrates having electrodes, at least one birefringent layer, and a pair of polarizing layers arranged so as to sandwich these layers from the outside. In a liquid crystal display element configured to at least include an electric signal by inputting an electric signal to the electrode to perform optical modulation, the retardation value of the liquid crystal layer and the retardation of the birefringent layer when the liquid crystal layer is aligned substantially parallel to the substrate. Sum of values (Δn
d) relates to a liquid crystal display device characterized by satisfying the formula (1).

[0008]

[Equation 3]

The present invention will be described in detail below. The liquid crystal layer sandwiched between the pair of substrates having the electrode of the present invention is a liquid crystal layer of a so-called driving cell which performs electric modulation by inputting an electric signal to the electrode. The liquid crystal drive cell of the present invention can be regarded as a kind of liquid crystal display element of a type in which liquid crystal molecules are darkly displayed when they are substantially parallel to the substrate and brightly displayed when they are substantially vertically aligned to the substrate. The present invention is not limited to this, and since the parameters can be corrected by the birefringent layer described below, there are few restrictions on the manufacturing conditions, and those having various retardations and twist angles can be used as the liquid crystal drive cell.

In the liquid crystal drive cell, the retardation of the liquid crystal layer (the product of the birefringence Δn ₁ and the thickness d ₁ , unit μm) when the liquid crystal molecules are oriented substantially parallel to the substrate satisfies the condition of the formula (2). It is desirable to satisfy.

[0011]

[Equation 4]

Here, θ ₁ is an absolute value (unit is degree) of the twist angle, and is usually 10 degrees or more and 380 degrees or less, preferably 25 degrees or more and 360 degrees or less. When the twist angle θ ₁ is 10 degrees or less, it is difficult to obtain a clear display, and when the twist angle θ ₁ is 380 degrees or more, it is necessary to set a large retardation according to the formula (2), and the viewing angle dependency of the display becomes large. .. The twist structure may be right twist or left twist,
It should be the same as the twist direction of the birefringent layer. If the condition of the expression (2) is not satisfied, the waveguide effect of the incident light does not appear and good optical modulation may not be performed, which is not preferable. Specific examples of the liquid crystal drive cell utilizing such a waveguide effect include a TN (twisted nematic) cell and an STN (super twisted nematic) cell.

The birefringent layer used in the present invention hardly changes its alignment structure even during display, and complements the parameters of the liquid crystal driving cell during dark display.
It is a part for optimizing the retardation and the twist angle of the display element of the present invention. Therefore, as such a birefringent layer,
It is appropriately selected depending on the liquid crystal driving cell to be used, and is not particularly limited, but it is desirable that the retardation of the birefringent layer (Δn ₂ d ₂ (unit: μm)) satisfy the condition of the expression (3).

[0014]

[Equation 5]

Here, θ ₂ is the absolute value (unit is degree) of the twist angle of the birefringent layer, and 5 degrees <θ <360 degrees, preferably 10 degrees <θ <300 degrees. Of course, the birefringent layer may be used alone or in two or more layers. When two or more birefringent layers are used, each birefringent layer preferably satisfies the formula (2). If this condition is not satisfied, the waveguide effect of incident light does not appear, and the parameters of the liquid crystal drive cell may not be sufficiently corrected, which is not preferable. The twisting direction of the birefringent layer needs to be the same as the twisting direction of the liquid crystal of the liquid crystal driving cell for light modulation. Examples of such a birefringent layer include a liquid crystalline polymer film (film) having a twisted nematic structure fixed thereon, a low-molecular liquid crystal layer having a twisted nematic structure sandwiched between a pair of transparent substrates, and the like. Among them, a liquid crystalline polymer film in which the twisted nematic orientation is fixed is preferably used in terms of orientation stability, which will be specifically described below.

As such a liquid crystalline polymer, those capable of immobilizing a twisted nematic structure in a liquid crystal state and then fixing the structure by cooling to a temperature below the glass transition point are preferable. Examples of such a liquid crystal polymer include a composition obtained by adding a predetermined amount of an optically active compound to a polymer liquid crystal that exhibits uniform and monodomain nematic alignment and can easily fix the alignment state. A polymer liquid crystal that exhibits a twisted nematic orientation such as a monodomain and that can easily fix the orientation state is mentioned.

First, the former composition comprising a nematic liquid crystal polymer and an optically active compound will be explained. A polymer which shows a uniform and monodomain nematic orientation as a base and can easily fix the orientation state. In the liquid crystal, in order to perform stable immobilization of nematic orientation, it is important in view of the phase sequence of the liquid crystal that it has no crystal phase at a temperature lower than that of the nematic phase. If these phases are present, they will inevitably pass through these phases when cooled for immobilization, and as a result the once obtained nematic orientation will be destroyed and the performance tends to be unsatisfactory. That is, it is preferable to use a polymer liquid crystal having a glass phase at a temperature lower than that of a nematic phase as a base. As the polymer liquid crystal, nematic alignment in the cholesteric liquid crystal state, all those that become glass state below the liquid crystal transition point can be used, for example, polyester, polyamide, polycarbonate, main chain liquid crystal polymer such as polyester imide, or polyacrylate, Examples thereof include side chain type liquid crystal polymers such as polymethacrylate, polymalonate, and polysiloxane. Among them, polyester is preferable from the viewpoint of easiness of synthesis, transparency, orientation, glass transition point and the like. The polyester used is most preferably a polymer containing an ortho-substituted aromatic unit as a constituent component, but an aromatic having a bulky substituent in place of the ortho-substituted aromatic unit, or an aromatic having a fluorine- or fluorine-containing substituent, etc. Polymers containing as a constituent can also be used. In the present invention, the ortho-substituted aromatic unit means a structural unit in which the bonds forming the main chain are in ortho positions with respect to each other.
Specific examples thereof include the following catechol units, salicylic acid units, phthalic acid units, and those having a substituent on the benzene ring of these groups.

[0018]

[Chemical 1] (X represents hydrogen, halogen such as Cl or Br, an alkyl group or an alkoxy group having 1 to 4 carbon atoms, or a phenyl group, and k is 0 to 2.) Of these, the following are particularly preferred examples. Such a thing can be illustrated.

[0019]

[Chemical 2]

By the way, as the polyester (a)
A structural unit derived from a diol (hereinafter referred to as a diol component) and a structural unit derived from a dicarboxylic acid (hereinafter referred to as a dicarboxylic acid component) and / or (b) one unit simultaneously contains a carboxylic acid and a hydroxyl group. Examples of the polymer include a structural unit derived from an oxycarboxylic acid (hereinafter referred to as an oxycarboxylic acid component) as a constituent, and preferably the ortho-substituted aromatic unit.

Among these, the following aromatic and aliphatic diols can be mentioned as the diol component.

[Chemical 3] (Y is hydrogen, halogen such as Cl and Br, and has 1 to 4 carbon atoms.
Represents an alkyl group, an alkoxy group, or a phenyl group. 1 is 0 to 2. ),

[0022]

[Chemical 4]

Above all,

[Chemical 5] And the like (wherein Me is a methyl group, Bu
Represents a butyl group).

The following can be exemplified as the dicarboxylic acid component.

[Chemical 6] (Z represents hydrogen, halogen such as Cl and Br, an alkyl group or an alkoxy group having 1 to 4 carbon atoms, or a phenyl group. M is 0 to 2.),

[0025]

[Chemical 7]

Above all,

[Chemical 8] Are preferred.

Specific examples of the oxycarboxylic acid component include the following units.

[Chemical 9]

The molar ratio of the dicarboxylic acid to the diol is approximately 1: 1 as in the case of general polyesters (in the case of using oxycarboxylic acid, the ratio of carboxylic acid group and hydroxyl group). The ratio of ortho-substituted aromatic units in the polyester is preferably in the range of 5 mol% to 40 mol%,
More preferably, it is in the range of 10 mol% to 30 mol%. When it is less than 5 mol%, a crystal phase tends to appear below the nematic phase, which is not preferable. 40 mol%
If the amount is larger, the polymer tends to lose liquid crystallinity, which is not preferable. The following polymers can be illustrated as a typical polyester.

[0029]

[Chemical 10] A polymer composed of structural units of

[0030]

[Chemical 11] A polymer composed of structural units of

[0031]

[Chemical formula 12] A polymer composed of structural units of

[0032]

[Chemical 13] A polymer composed of structural units of

[0033]

[Chemical 14] A polymer composed of structural units of

[0034]

[Chemical 15] A polymer composed of structural units of

[0035]

[Chemical 16] A polymer composed of structural units of

[0036]

[Chemical 17] A polymer composed of structural units of.

Polymers having an aromatic unit containing a bulky substituent as shown below instead of an ortho-substituted aromatic unit, or a polymer containing an aromatic unit containing a fluorine- or fluorine-containing substituent as a constituent component are also preferably used.

[0038]

[Chemical 18]

[0039]

[Chemical 19]

The molecular weight of these polymers can be determined in various solvents such as phenol / tetrachloroethane (60/40).
Weight ratio) In a mixed solvent, the logarithmic viscosity measured at 30 ° C. is 0.
05 to 3.0 is preferable, and 0.0 is more preferable.
It is in the range of 7 to 2.0. If the logarithmic viscosity is less than 0.05, the strength of the obtained polymer liquid crystal may be weak. If the logarithmic viscosity is more than 3.0, the viscosity at the time of liquid crystal formation is too high, resulting in a decrease in orientation and alignment. There may be problems such as an increase in the time required. Further, the glass transition point of these polyesters is also important and affects the stability of orientation after the orientation is fixed. Although depending on the application, the glass transition point is usually 0 ° C. or higher, preferably 10 ° C. or higher, and generally, when the glass transition temperature is considered to be around room temperature, the glass transition point is 3 or less.
The temperature is preferably 0 ° C or higher, and particularly preferably 50 ° C or higher. If the glass transition temperature is lower than 0 ° C,
When used near room temperature, the once fixed liquid crystal structure may change, and the function derived from the liquid crystal structure may deteriorate.

The method for synthesizing these polymers is not particularly limited, and they can be synthesized by a polymerization method known in the art, for example, a melt polymerization method or an acid chloride method using a corresponding acid chloride of dicarboxylic acid. In the case of synthesizing by a melt polymerization method, for example, it can be produced by polymerizing an acetylated product of a corresponding dicarboxylic acid and a corresponding diol at high temperature under high vacuum, and the molecular weight can be easily controlled by controlling the polymerization time or controlling the charging composition. ..
In order to accelerate the polymerization reaction, a conventionally known metal salt such as sodium acetate can also be used. When the solution polymerization method is used, the desired polyester can be easily obtained by dissolving a predetermined amount of dicarboxylic acid dichloride and diol in a solvent and heating in the presence of an acid acceptor such as pyridine.

The optically active compound which is mixed to impart twist to these nematic liquid crystalline polymers will be explained. As a typical example, an optically active low molecular weight compound can be mentioned first. Any compound having an optical activity can be used in the present invention, but an optically active liquid crystal compound is preferable from the viewpoint of compatibility with the base polymer. Specifically, the following compounds can be exemplified.

[0043]

[Chemical 20]

[0044]

[Chemical 21]

Examples of the optically active compound used in the present invention include the following optically active polymer compounds. Any polymer can be used as long as it has an optically active group in the molecule, but a polymer showing liquid crystallinity is preferable from the viewpoint of compatibility with the base polymer. Examples thereof include liquid crystal polyacrylates, polymethacrylates, polymalonates, polysiloxanes, polyesters, polyamides, polyesteramides, polycarbonates having an optically active group, polypeptides, and celluloses. Among them, an optically active polyester mainly containing an aromatic compound is most preferable because of its compatibility with the nematic liquid crystal polymer as the base. Specifically, the following polymers can be exemplified.

[0046]

[Chemical formula 22] A polymer composed of the structure of

[0047]

[Chemical formula 23] A polymer composed of structural units of

[0048]

[Chemical formula 24] A polymer composed of structural units of

[0049]

[Chemical 25] A polymer composed of structural units of

[0050]

[Chemical formula 26] A polymer composed of structural units of

[0051]

[Chemical 27] A polymer composed of structural units of

[0052]

[Chemical 28] A polymer composed of structural units of

[0053]

[Chemical 29] A polymer composed of structural units of

[0054]

[Chemical 30] A polymer composed of structural units of

[0055]

[Chemical 31] A polymer composed of structural units of

[0056]

[Chemical 32] A polymer composed of structural units of.

The proportion of the optically active group in these polymers is usually 0.5 mol% to 80 mol%, preferably 5 mol% to 60 mol%.

The molecular weight of these polymers is preferably such that the logarithmic viscosity measured at 30 ° C. in phenol / tetrachloroethane is in the range of 0.05 to 5.0.
If the logarithmic viscosity is more than 5.0, the viscosity is too high, resulting in a decrease in orientation, which is not preferable.
When it is less than 5, the composition is difficult to control, which is not preferable.

These compositions can be prepared by a method such as fixed mixing, solution mixing or melt mixing of the nematic liquid crystal polyester and the optically active compound in a predetermined ratio. The ratio of the optically active compound in the composition varies depending on the ratio of the optically active group in the optically active compound or the twisting force when the nematic liquid crystal of the optically active compound is twisted, but it is generally 0. 1 to 30
The range of wt% is preferable, and the range of 0.3 to 20 wt% is particularly preferable. If the amount is less than 0.1 wt%, the nematic liquid crystal cannot be sufficiently twisted.
When it is more than 0 wt%, the twist becomes too large and the orientation is adversely affected.

On the other hand, as a polymer liquid crystal capable of performing uniform and monodomain twisted nematic alignment by itself and easily fixing the alignment state without using the other optically active compound of the latter, the polymer main chain is It is essential that the compound itself has an optically active group and is optically active. Specifically, the main chain type liquid crystal polymer such as optically active polyester, polyamide, polycarbonate, polyesterimide, or polyacrylate, polymethacrylate, or polyacrylate. Examples thereof include side chain type liquid crystal polymers such as siloxane. Among them, polyester is preferable from the viewpoint of easiness of synthesis, orientation, glass transition point and the like. The polyester used is most preferably a polymer containing an ortho-substituted aromatic unit as a constituent component, but an aromatic having a bulky substituent in place of the ortho-substituted aromatic unit, or an aromatic having a fluorine- or fluorine-containing substituent, etc. Polymers containing as a constituent can also be used. These optically active polyesters can be obtained by introducing the following optically active groups to the nematic liquid crystalline polyesters described so far using an optically active diol, dicarboxylic acid or oxycarboxylic acid.
(In the formula, * indicates optically active carbon)

[0061]

[Chemical 33]

[0062]

[Chemical 34]

The proportion of these optically active groups in the polymer is preferably in the range of 0.1 to 20 mol%, particularly preferably in the range of 0.3 to 10 mol%. If the proportion of the optically active group is less than 0.1%, a twisted structure cannot be obtained, and if it exceeds 20 mol%, the orientation is adversely affected, which is not preferable. The molecular weight of these polymers can vary in various solvents such as phenol / tetrachloroethane (60
/ 40) The logarithmic viscosity measured at 30 ° C. in a mixed solvent is 0.
05 to 3.0 is preferable, and 0.07 is more preferable.
To 2.0. If the logarithmic viscosity is less than 0.05, the strength of the obtained polymer liquid crystal becomes weak, which is not preferable. On the other hand, when it is more than 3.0, the viscosity at the time of forming the liquid crystal is too high, which causes problems such as deterioration of alignment property and increase of time required for alignment. The glass transition point of these polyesters is usually 0 ° C or higher, preferably 10 ° C, though it depends on the use.
As described above, it is desirable that the glass transition point is 30 ° C. or higher, in general, considering that the glass transition temperature is around room temperature.
It is desirable that the temperature is ℃ or higher. When the glass transition point is lower than 0 ° C., the liquid crystal structure once immobilized may change when used near room temperature, and the function derived from the liquid crystal structure deteriorates, which is not preferable. Polymerization of these polymers can be carried out by using the above-mentioned melt polymerization method or acid fluoride method.

As typical examples of the liquid crystalline polymer of the present invention described above, specifically,

[Chemical 35] Ch: cholesteryl group, a polymer (m / n =
Usually 99.97 / 0.03 to 80/20, preferably 9
9.9 / 0.1-90 / 10),

[0065]

[Chemical 36] Polymer (m / n = usually 99.97 / 0.0
3-80 / 20, preferably 99.9 / 0.1-90 /
10),

[0066]

[Chemical 37] (M / n = usually 99.96 / 0.0
4 to 70/30, preferably 99.9 / 0.1 to 90 /
10, p, q: an integer of 2 to 20),

[0067]

[Chemical 38] (M / n = usually 99.96 / 0.0
4 to 70/30, preferably 99.9 / 0.1 to 90 /
10, p, q: an integer of 2 to 20)

[0068]

[Chemical Formula 39] (M / n = usually 99.98 / 0.
02-80 / 20, preferably 99.9 / 0.1-90
/ 10, more preferably 99.8 / 0.2 to 95 /
5)

[0069]

[Chemical 40] (M / n = 0.1 / 99.9-10)
/ 90, preferably 0.2 / 99.8 to 5/95)

[0070]

[Chemical 41] (K = 1 / m + n, k / n = 99.
96 / 0.04 to 90/10, preferably 99/1 to
95/5, 1 / m = 5/95 to 95/5, R ₁ and R ₂ are H, Cl or a linear or branched alkyl group having 1 to 6 carbon atoms)

[0071]

[Chemical 42] (K = 1 / m + n, k / n = 99.
96 / 0.04 to 90/10, preferably 99/1 to
95/5, 1 / m = 5/95 to 95/5, R ₁ and R ₂ include H, Cl, or a straight-chain or branched alkyl group having 1 to 6 carbon atoms).

[0072]

[Chemical 43] Polymer mixture represented by ((A) / (B) = normally 9
9.97 / 0.03 to 80/20 (weight ratio), preferably 99.9 / 0.1 to 85/15, k = 1 + m, 1 / m
= 85/15 to 15/85, p = q + r, r / q = 0 /
100 to 80/20, R ₁ and R ₂ are H, Cl or a linear or branched alkyl group having 1 to 6 carbon atoms)

[0073]

[Chemical 44] Polymer mixture represented by ((A) / (B) = normally 9
9.95 / 0.05 to 70/30 weight ratio, preferably 9
9.9 / 0.1-80 / 20, preferably 99.9 /
0.1-90 / 10, m = k + 1, k / l = 80/20
~ 20/80)

[0074]

[Chemical 45] Polymer mixture represented by ((A) / (B) = normally 9
9.97 / 0.03 to 75/25 (weight ratio), preferably 99.9 / 0.1 to 85/15, k = 1 + m, 1 / m
= 25/75 to 75/25, p = q + r, q / r = 20
/ 80 to 80/20, R ₁ , R ₂ , and R ₃ are H, Cl, or a linear or branched alkyl group having 1 to 6 carbon atoms) (Note that * indicates an optically active asymmetric carbon), etc. Is mentioned.

The liquid crystalline polymer or the composition containing the liquid crystalline polymer is dissolved in a suitable solvent and applied on a transparent substrate having an alignment film. Although the kind of the alignment film is not particularly limited, it may be any one as long as it aligns the liquid crystal molecules in parallel with the interface. For example, a rubbed polyimide film is preferably used. Of course, an alignment film known in the art such as a rubbing film of alcohol can be used. After coating, the solvent is removed by drying, and heat treatment is performed at a predetermined temperature for a predetermined time to complete the twisted nematic orientation of the monodomain, and then the orientation is fixed by cooling to a temperature not higher than the glass transition point of the liquid crystalline polymer. The birefringent layer used in the present invention is prepared. A birefringent layer having a similar orientation can also be obtained by applying a polymer in a molten state onto an orientation-treated substrate and then performing heat treatment and cooling.
Further, the film-shaped birefringent layer may be separately prepared and used in combination.

The polarizing layer used in the present invention is not particularly limited as long as it can convert natural light into linearly polarized light. For example, a polyvinyl alcohol film impregnated with iodine molecules is used. A polarizing plate or the like on the sheet is preferably used.

The liquid crystal display device of the present invention is basically constructed by laminating the above-mentioned light modulating liquid crystal cell and at least one birefringent layer, and sandwiching this by a pair of polarizing layers. Retardation (Δn ₁ d ₁ ) of the display cell for light modulation when the substrate is substantially parallel to the substrate and retardation (Δn ₂ ) of the birefringent layer.
d ₂ and the sum (Δnd) with two or more layers),
It almost matches the retardation of the entire liquid crystal display element during dark display, and in order to obtain good dark display or high contrast, it is necessary to satisfy the following formula.

[0078]

[Equation 6]

Here, λ is the wavelength of the light that is almost not transmitted during black display, and 0.45 μm <λ <0.65 μm.
Is. k is an integer of an order which normally satisfies 1 ≦ k ≦ 4, preferably 1, 2 or 3. θ (unit is degrees) is the sum of the twist angles of the liquid crystal layer and the birefringent layer, and
Degree <θ <400 degrees, preferably 20 degrees <θ <400 degrees,
More preferably, 30 ° <θ <380 °. k is 5
In the above cases, the retardation value of the entire liquid crystal display element becomes too large, and the contrast decreases drastically depending on the viewing angle. When θ is 15 degrees or less, a clear display cannot be obtained, and when it is 400 degrees or more, the thickness of the liquid crystal layer and / or the birefringent layer is satisfied in order to satisfy the conditions of the formulas (2) and (3). Must be made large, the retardation of the entire liquid crystal display element becomes too large, and the contrast is drastically lowered depending on the viewing angle. However, in the formula (1 ′), k
When ≦ θ / 180, Δnd becomes 0 or an imaginary number and has no meaning, so that k> θ / 180,
Actually, k ≧ 1 when 15 ° <θ <180 °,
When 180 ° ≦ θ <360 °, k ≧ 2, and 360 ° ≦
When θ <400 degrees, k ≧ 3. In addition, this formula (1 ')
The physical meaning of is that the retardation Δnd, which can make the leakage of light of a specific wavelength λ almost zero in black display at a certain twist angle θ, can take only discrete values determined by the order k. Is. However, the wavelength of light for which the leakage should be almost zero cannot be uniquely determined because there are some individual differences in the purpose of use, taste, or how to perceive the wavelength of light.

The position of the birefringent layer may be anywhere between a pair of polarizers, and may be located above or below the liquid crystal driving cell. On the surface where the liquid crystal driving cell and the birefringent layer are in contact with each other, it is necessary that the long-axis direction of the liquid crystal molecules of the liquid-crystal driving cell and the long-axis direction of the birefringent layer are substantially aligned or substantially orthogonal to each other. For example, when a birefringent layer of a liquid crystalline polymer is provided on the upper surface of a liquid crystal driving cell, the alignment direction of the liquid crystal molecules at the top of the liquid crystal cell during substantially parallel alignment with the substrate and the alignment direction of the molecules at the bottom of the polymer liquid crystal layer However, the angle should be approximately 0 degrees or 90 degrees. Further, when the birefringent layers are successively laminated, the birefringent layers are arranged such that the orientation directions at the interfaces are substantially parallel or substantially orthogonal. The liquid crystal driving cell and the birefringent layer accumulated are sandwiched by a pair of polarizers, and a light source for display is placed on either side of the polarizers to complete the liquid crystal display element of the present invention.

The liquid crystal display device thus obtained is
A color compensator can be incorporated to further improve the contrast, or a color display can be produced by combining with a color filter. Examples of the color compensator include liquid crystal polymer films having the same retardation value as that of the liquid crystal display element of the present invention and the same twisted nematic structure with the same twist angle but opposite directions. It is also possible to incorporate an element for further improving the viewing angle.

The liquid crystal display device of the present invention obtained as described above has a high response speed and a small viewing angle dependency of contrast, and therefore, it is used for display for all kinds of displays including displays for liquid crystal televisions for displaying moving images. It has a great industrial value.

[0083]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Example 1 The total twist angle was 180 degrees, and the light transmittance during black display was 55.
It becomes a minimum at 0 nm, and the order k in equation (1 ′)
In order to obtain a liquid crystal display device having a value of 2, the following liquid crystal drive cell and birefringent layer were produced.

(Liquid crystal drive cell) A nematic liquid crystal ZLI-229 manufactured by Merck & Co. having positive dielectric anisotropy between two substrates having a transparent electrode and an alignment film (gap of 2.0 μm).
3 (birefringence 0.13) was enclosed, and a liquid crystal drive cell with a retardation of 0.26 μm and a left twist of 90 ° was produced.

(Birefringent layer) 15% by weight of the polymer represented by the following formula (4) on a glass substrate having a rubbed polyimide film.
The tetrachloroethane solution of is applied by spin coating,
After drying, the film was heat-treated at 200 ° C. and cooled to prepare a film in which a retardation of 0.69 μm and a 90 ° left-handed nematic structure were fixed.

The sum of these retardations is 0.95.
μm, the sum of twist angles is 180 degrees, k = 2, λ =
As 0.55, the equation (1 ′) can be satisfied.

By laminating these, a liquid crystal display device having the structure shown in FIG. 1 was produced. For comparison, a cell with 90 ° left twist and a retardation of 1.06 μm (Zwisted nematic cell) enclosing ZLI-2293 with a gap of 8.0 μm was manufactured and used in the configuration of FIG. Responded faster. Further, in any of the configurations, when a non-voltage is applied, a high-quality display in a dark state with almost no transmission of light having a wavelength of 550 nm was obtained. However, the display element of FIG. 2 is different from the display element of FIG. The leak was noticeable.

[0088]

[Chemical 46] However, * represents an asymmetric carbon, and the 2-methylbutanediol unit is R-form.

[0089] In the configuration of FIG. 1 Comparative Example 1 Example 1 was produced different display elements only retardation of the birefringent layer. The liquid crystal driving cell used was the same as that of the embodiment shown in FIG.

The birefringent layer has a retardation of 0.5.
When a liquid crystal display device of 0 μm (90 ° left twist) was used, the total retardation of the liquid crystal display element was 0.76 μm, the total twist angle was 180 °, and k = 2 in the formula (1 ′), so λ = 0. 44 μm, and 0.45 μm <λ <0.
Although the condition of 65 μm was not satisfied, in actuality, a large amount of light leaked during dark display, resulting in a reddish color, and a good display could not be obtained.

Further, the retardation of the birefringent layer is 0.
In the case of 91 μm (90 ° left twist), the dark display became bluish and no good display was obtained.

[0092]

Since the liquid crystal display device of the present invention is composed of the liquid crystal driving cell for light modulation and the birefringent layer, the design of optical parameters is easy and the response speed is high.
It is possible to perform a display in which the contrast is less dependent on the viewing angle, and is of great industrial value that can be used as a display for any display purpose, such as a display for a liquid crystal television that displays a moving image.

[Brief description of drawings]

FIG. 1 shows the configuration of a liquid crystal display element used in Example 1 of the present invention and the orientation of each axis of the constituent material.

FIG. 2 shows a block diagram of a TN cell used in Example 1 for comparison.

[Explanation of symbols]

 1 Lower polarizing plate 2 Liquid crystal driving cell 3 Birefringent layer 4 Upper polarizing plate 5 Polarization axis direction 6 Rubbing direction of lower electrode substrate of liquid crystal cell 7 Rubbing direction of upper electrode substrate of liquid crystal cell 8 Rubbing direction of alignment substrate of birefringent layer 9 Orientation direction of the uppermost molecule of the birefringent layer

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[Procedure amendment]

[Submission date] September 25, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

[0044]

[Chemical 21]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0064

[Correction method] Change

[Correction content]

As typical examples of the liquid crystalline polymer of the present invention described above, specifically, Ch: cholesteryl group, a polymer (m / n =
Usually 99.97 / 0.03 to 80/20, preferably 9
9.9 / 0.1-90 / 10),

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

Claims (1)

[Claims] 1. A liquid crystal layer sandwiched between a pair of substrates having electrodes, at least one birefringent layer, and a pair of polarizing layers arranged so as to sandwich these layers from the outside. , In a liquid crystal display element that performs an optical modulation by inputting an electric signal to the electrode, the sum of the retardation value of the liquid crystal layer and the retardation value of the birefringent layer when the liquid crystal layer is aligned substantially parallel to the substrate ( Δnd) satisfies the formula (1), a liquid crystal display device. [Equation 1]