JPH0750269B2 - Liquid crystal device - Google Patents

Description

The present invention relates to a liquid crystal device, and more particularly to a super twisted nematic liquid crystal device.

[Conventional technology]

Conventional super twisted nematic type (hereinafter STN
The liquid crystal device of the type) has a twist angle of liquid crystal molecules of 90 degrees or more as disclosed in JP-A-60-50511, and a pair of polarizing plates are provided above and below the liquid crystal cell. )
And the angle formed by the molecular axis direction of the liquid crystal molecules adjacent to the electrode substrate was in the range of 30 to 60 degrees. Therefore, due to the birefringence coloring, the hue of the appearance when no voltage is applied to the liquid crystal cell is not white, but is generally a hue from green to yellow-red. In addition, the hue of the appearance when the selection voltage is applied is generally blue instead of black.

FIG. 29 is a schematic view of a conventional STN type liquid crystal device. In the figure, 101 is a lower polarizing plate, 102 is an upper polarizing plate, 110 is a liquid crystal cell, and a liquid crystal layer is provided between a lower substrate 111 and an upper substrate 112.
It has a structure in which 113 is sandwiched. A transparent electrode 114 such as an ITO electrode is formed on each of the facing surfaces of the two substrates 111 and 112, and an alignment film 115 is further applied and subjected to a rubbing treatment. 116 is a spacer.

FIG. 30 is an explanatory diagram showing the relationship between the liquid crystal cell and the polarization axis (absorption axis) of the polarizing plate in the above liquid crystal device, in which R1 is the rubbing direction of the lower electrode substrate of the liquid crystal cell, and R2 is the liquid crystal. The rubbing direction of the upper electrode substrate of the cell, P1 is the direction of the polarization axis (absorption axis) of the lower polarizing plate, P2 is the direction of the polarization axis (absorption axis) of the upper polarizing plate, and t is the twist angle of the liquid crystal molecules of the liquid crystal cell. , Α1 is the angle between the rubbing direction R1 of the lower electrode substrate and the polarization axis (absorption axis) direction P1 of the lower polarizing plate, α2 is the rubbing direction R2 of the upper electrode substrate and the polarizing axis of the upper polarizing plate. It represents the angle formed by the (absorption axis) direction P2.

In FIG. 30, the angle t is 200 degrees, and the angles α1 and α2 are
FIG. 31 shows the optical characteristics of the liquid crystal device when the product Δn · d of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer is 0.9 μm.

The figure shows a positive mode (bright when no voltage is applied) on-state pixel and an off-state pixel when the liquid crystal device is driven by a multiplex drive method which is usually used as a drive method for this type of liquid crystal device. It is what shows the spectrum of the light transmittance of the pixel of the state.

In this document, the off state refers to a state in which no electric field is applied, or the state in which almost no voltage is applied is maintained even when an electric field is applied, and the on state refers to a change in the liquid crystal molecular orientation. Is necessary and sufficient to cause an optical change.

The curve I in FIG. 31 shows the spectrum of the pixel in the off state, and the curve II shows the spectrum of the pixel in the on state.
Is "bright" curve II is "dark", ie curves I and II
It can be seen that can be visually distinguished.

[Problems to be Solved by the Invention]

However, when the spectrum shown in FIG. 31 is plotted on the color coordinates, it becomes as shown in FIG. 32. In the conventional liquid crystal device, the off state is colored yellow in the positive mode and blue in the on state. I understand.

As described above, in the related art, the appearance color of the liquid crystal device in the off state is colored green, yellow-green, yellow, or yellow-red in the positive mode, and blue or navy blue in the on-state. In the negative mode (dark when no voltage is applied), it is dark blue in the off state and yellow in the on state.

These colors are not the colors generally preferred as the display colors of liquid crystal devices. After all, the display color of the liquid crystal device is a combination of white and black, that is, if it is shown by a spectrum,
Since the combination of flat spectra is the most suitable psychologically and physically, a liquid crystal device capable of displaying black and white is required. In particular, when performing color display by combining with a color filter, whether or not the spectrum is flat greatly affects the vividness of the color, and in the conventional method shown in the spectrum in FIG. 31, Apart from green, it is difficult to display blue and red with high brightness.

By the way, as a means for eliminating the above-mentioned coloring, in a twisted nematic type (hereinafter referred to as TN type) liquid crystal device, a twisted nematic liquid crystal layer in which a power feeding means is not provided in a single layer type twisted nematic field effect liquid crystal display cell is used. A liquid crystal device having a two-layer structure in which the layers are superposed is known (see, for example, JP-A-57-96315).

However, the liquid crystal device disclosed in the above publication is not directly applicable to the STN type liquid crystal device described above.

That is, the liquid crystal device described in the above publication is a so-called TN type. That is, the twist angle is 90 degrees, and the polarizing plates are arranged in parallel or orthogonal to the directions of the adjacent liquid crystal molecules, and the operating principle thereof utilizes the optical rotatory power. Therefore, the structure is significantly different from the STN type structure in which birefringence is positively used in the operation principle, and therefore cannot be simply applied to the STN type liquid crystal device as it is.

The present invention solves the above problems, and an object of the present invention is to provide a liquid crystal device capable of monochrome display, and further to provide a liquid crystal device suitable for color display.

[Means for Solving the Problems]

In order to achieve the above object, the liquid crystal device according to the present invention has the following configuration.

That is, a display cell formed by sandwiching a first nematic liquid crystal layer twisted and oriented at 120 ° or more between a pair of substrates having electrodes formed on opposing inner surfaces, and at least one optical anisotropic body. The second nematic liquid crystal layer is provided between the pair of polarizing plates, and the polarization axis direction of each polarizing plate is substantially parallel to the long axis direction of the liquid crystal molecules of the display cell or the second nematic liquid crystal layer adjacent to the polarizing plate. Or, the light which is set in a predetermined direction excluding the substantially orthogonal direction and is incident on one polarizing plate is
Elliptically polarized light having a different major axis direction for each wavelength is formed between the display cell and the second nematic liquid crystal layer adjacent to the display cell, and when the light is incident on the other polarizing plate, a long wavelength is obtained for each wavelength. According to the twist angle of the first nematic liquid crystal layer and the value of Δn · d, the twist angle of the second nematic liquid crystal layer and Δn ·
The value of d is set to a predetermined value so as to eliminate display coloring in the ON state and the OFF state of the display cell, and the temperature of the NI point of the first nematic liquid crystal layer is set to
T ₁ (° K), the temperature at the NI point of the second nematic liquid crystal layer is T ₂
It is characterized by using a liquid crystal such that 0.86 ≦ T ₂ / T ₁ ≦ 1.15 when (° K).

[Work]

As described above, a display cell in which a first nematic liquid crystal layer twisted and oriented at 120 ° or more is sandwiched between a pair of substrates having electrodes formed on the inner surfaces facing each other, and at least one optical anisotropic body A certain second nematic liquid crystal layer is provided between a pair of polarizing plates, and light incident on one polarizing plate is
When the display cell and the second nematic liquid crystal layer adjacent to the display cell become elliptically polarized light having a different major axis direction for each wavelength, and then enter the other polarizing plate, the major axis for each wavelength The twist angle and Δn · d of the second nematic liquid crystal layer are adjusted in accordance with the twist angle of the first nematic liquid crystal layer and the value of Δn · d so as to obtain elliptically polarized light whose directions are substantially aligned.
Is set to a predetermined value to eliminate the coloring of the display in the ON state and the OFF state of the display cell, so that the STN type liquid crystal device can be colored as described above as much as possible. It becomes possible to reduce.

The temperature of the liquid crystal NI point of the second nematic liquid crystal layer is set to T ₂
(° K), when the temperature at the NI point of the liquid crystal of the display cell is T ₁ (° K), by using the liquid crystal such that 0.86 ≦ T ₂ / T ₁ ≦ 1.15, the display cell and the second It is possible to prevent the appearance color of the liquid crystal device from changing even if Δn · d of the nematic liquid crystal layer changes.

〔Example〕

FIG. 1 is a sectional view showing a schematic configuration of a liquid crystal device according to the present invention.

In the figure, 1 is a lower polarizing plate, 2 is an upper polarizing plate, and 10 is a display cell having a first nematic liquid crystal for displaying by applying a voltage. A liquid crystal layer 13 is interposed between a pair of upper and lower substrates 12 and 11. It has a different structure. Reference numeral 20 denotes a liquid crystal cell for color correction (hereinafter referred to as a compensation cell) having a second nematic liquid crystal layer which is an optically anisotropic body, and has a structure in which a liquid crystal layer 23 is interposed between a pair of upper and lower substrates 22 and 21. is there.

The polarizing plate, liquid crystal material, liquid crystal alignment method, liquid crystal element driving method and the like used in the present invention can be the same as those generally known in conventional TN type or STN type liquid crystal devices and the like. Is. The details will be described below.

The optical characteristics are greatly affected by the polarization characteristics of the polarizing plate used. In the specific examples of the present invention, LLC2-82-18 manufactured by Sanritsu Electric Co., Ltd. is used in all, but it goes without saying that the present invention is not limited to this. FIG. 3 shows the wavelength dependence of the light transmittance of the two polarizing plates. In the figure, I is a spectrum curve when a pair of polarizing plates are arranged parallel to each other, and II is a spectrum curve when they are arranged perpendicularly to each other.

The liquid crystal composition used in the present invention is a nematic liquid crystal having a positive dielectric anisotropy. An example of a preferable liquid crystal is SS-4008 manufactured by Chisso Corporation. The following is also an example of another preferable liquid crystal composition.

A chiral dopant is preferably added to the liquid crystal composition in order to keep the twisted structure of the liquid crystal stable.

As the chiral dopant, for example, CB-15 manufactured by BDH can be used to obtain a right-handed helical structure, and S-811 manufactured by Merck can be used to form a left-handed helical structure.

The structure of the display cell 10 used in the present invention may be the same as that of the liquid crystal cell 110 used in the prior art shown in FIG. 29.

As the substrates 11, 12, 21 and 22 of the display cell 10 and the compensation cell 20, transparent substrates such as glass and plastic are used. On the substrate of the display cell 10, a transparent electrode such as ITO and an alignment film layer that determines the alignment of liquid crystal are formed on the transparent electrode. If necessary, a transparent electrode is provided on the substrate of the compensation cell 20, and an alignment film layer is formed on the electrode or the substrate.

Polyimide, polyvinyl alcohol and the like are preferable examples of the alignment film layer. Generally, by rubbing these alignment film layers, the liquid crystal can be given a certain alignment. Further, as another method of aligning the liquid crystal, an oblique vapor deposition method of SiO or the like can be used.

An example of the driving method of the liquid crystal device of the present invention is shown in FIG. The multiplex driving method shown in the figure is a method that is generally used at present and has been put to practical use, but other driving methods can be used in the present invention.

A nematic liquid crystal is used as the liquid crystal of the compensation cell used in the present invention. Further, it is also desirable to use the same nematic liquid crystal as the display cell.

Next, the basic role of the compensation cell 20 will be described in comparison with the conventional STN type liquid crystal device.

FIG. 33 is an explanatory diagram of the optical characteristics in the off state of the conventional STN type liquid crystal device in FIG. 29, in which L is the incident light. The incident light L is generally natural light, includes light of all wavelengths in the visible region, and has a random polarization direction. When the incident light L passes through the linear polarization plate 101, it becomes a set of linearly polarized lights b51, g51, r51, etc., in which the polarization directions are aligned. Where b5
1, g51 and r51 represent polarized light having wavelengths of 450 nm, 550 nm and 650 nm, respectively. Of course, linearly polarized light of other wavelengths is also included,
Here, only these three wavelengths are shown as the representative wavelengths of the three colors of blue, green and red. These linearly polarized light b51 ・ g51 ・ r5
The 1 then passes through the liquid crystal cell 110. The liquid crystal layer in the liquid crystal cell has a structure in which nematic liquid crystals exhibiting optically uniaxial refractive index anisotropy are twisted. Regarding how the polarization state changes when the linearly polarized light b51, g51, r51, etc. passes through the liquid crystal layer having such a structure,
It can be predicted by the method described later. For example, when the results of the above-mentioned conventional liquid crystal device whose spectrum is shown in FIG. 31 are shown, the polarization states are b52, g52, and r52, respectively, as shown in FIG. By passing through the liquid crystal layer in this way, wavelength dispersion occurs in the polarization state. These polarized lights b52, g52, and r52 finally pass through the linear polarization plate 102.
As for the polarized light of each wavelength, only the component corresponding to the direction of the linear polarizing plate 102 passes through. For example, in the above-mentioned conventional liquid crystal device whose spectrum is shown in FIG. 31, each of b53 and g53
・ It becomes like r53. The amount of light of wavelength 550nm is larger than this,
It can be seen that the amount of light at wavelengths of 450 nm and 650 nm is small. A spectral representation of these results is I in FIG. 31, and a plot of this on color coordinates is I in FIG. As described above, the conventional STN type liquid crystal display device had to be colored due to wavelength dispersion due to birefringence.

Next, FIG. 5 shows an explanatory view of the optical characteristics of the liquid crystal device according to the present invention in the off state. Comparing FIGS. 33 and 5 with each other, FIG. 5 shows that in addition to the display cell 10, a compensation cell 20 having a second nematic liquid crystal layer which is an optically anisotropic body is added as a constituent element. 33 different from the figure. For convenience of explanation, the conditions of the components other than the compensation cell 20 and the polarizing plate 2 are the same as those of the conventional example shown in FIG. 33, that is, the liquid crystal device whose spectrum is shown in FIG. And

Therefore, in FIG. 5, the polarization states b2, g2, r2 of the respective wavelengths after passing through the display cell 10 via the polarizing plate 1 are represented by b5 in FIG.
It is exactly the same as 2 ・ g52 ・ r52. The difference is that it is the compensation cell 20 through which each of the polarized lights b2, g2, r2 in FIG. In the present invention,
The compensation cell 20 has the function of canceling the chromatic dispersion generated by the linearly polarized light b1, g1, and r1 by the polarizing plate 1 passing through the display cell 10.

The optical function of the display cell 10 is defined as M in order to explain this action in an easy-to-understand manner. Further, if the polarization state of b1 · g1 · r1 is P and the polarization state of b2 · g2 · r2 is P ′, then P ′ is P
And M are calculated by the following equation.

P ′ = M * P (1) Here, a function for performing an inverse transformation of M on the optical function of the compensation cell 20.
Assume that it is M ^-1 . Assuming that the polarization state of b3 · g3 · r3 is P ″, P ″ is obtained from P ′ and M ⁻¹ by the following equation.

P ″ = M ⁻¹ * P ′ (2) The following equation is obtained from the equations (1) and (2).

P ″ = M ⁻¹ * M * P (3) Clearly M ⁻¹ * M = 1 (4) Therefore, P ″ = P (5) (5) is the polarization state (P ″)
It is shown that it is the same as the polarization state (P) of b1, g1, and r1. Since b1, g1, and r1 are polarized light immediately after the natural light L has passed through the linear polarizing plate 1, all wavelengths are linear polarized light having a vibration direction corresponding to the azimuth of the polarizing plate 1. Therefore b3 ・ g3
・ R3 is also a linearly polarized light whose vibration direction is in the same direction as b1, g1, and r1. Polarization axis direction of linear polarizing plate 1 is polarized light b3 ・ g3 ・ r3
When the vibration direction is coincident with the vibration direction of, the linearly polarized light passes through the linearly polarizing plate 2 as it is and becomes b4, g4, and r4.

The spectrum of the emitted light at this time matches the spectrum of the polarizing plate shown in I of FIG. 3 (however, the light absorption in the display cell and the compensation cell etc. is ignored). The spectrum of the polarizing plate is almost flat and colorless. As described above, the liquid crystal device according to the present invention can eliminate the coloring phenomenon in the off state.

Although the main points of the present invention are as described above, the problem is that the compensation which can perform the reverse conversion of the conversion performed by the display cell 10 on the linearly polarized light b1, g1, r1, etc. incident on the display cell 10 in FIG. It is whether the cell can actually exist. In conclusion, we have found that such a compensating cell 20 condition may exist. Moreover, it has been found that such a condition can exist regardless of the condition of the display cell 10.

In order to explain this condition, the relationship between each cell and the polarizing plate in the liquid crystal device of the present invention shown in FIG. 1 is shown in FIG.

In the figure, P1 and P2 are directions of polarization axes (absorption axes) of the lower polarizing plate 1 and the upper polarizing plate 2, respectively, and R11 and R12 are display cells.
Rubbing direction of lower substrate 11 and upper substrate 12 of R10 and R22
Is the rubbing direction of the lower substrate 21 and the upper substrate 22 of the compensation cell 20, t1 is the twist angle and direction of the liquid crystal of the display cell 10, t2 is the twist angle and direction of the liquid crystal of the compensation cell 20, and α1 is the lower polarizing plate. The angle between the direction P1 of the polarization axis and the rubbing direction R11 of the lower substrate of the display cell, α2 is the angle between the direction P2 of the polarization axis of the upper polarizing plate and the rubbing direction R22 of the upper substrate of the compensation cell, and β is the compensation It is an angle formed by the rubbing direction R21 of the lower substrate of the cell and the rubbing direction R12 of the upper substrate of the display cell. The twist direction of the liquid crystal molecules in each cell is the twist direction from the top to the bottom of the cell. The same applies hereinafter.

Here, for example, the conditions of the display cell are exactly the same as those of the conventional positive mode liquid crystal device whose spectrum is shown in FIG. 31, that is, the twist angle t1 of the liquid crystal layer in the display cell is 200.
The whitening condition when Δn · d is 0.9 μm will be described. When there is no compensation cell, the spectrum naturally becomes as shown in FIG. 31 and is in a colored state. However, if a compensating cell is used and the twist angle t2 of the liquid crystal layer is −200 degrees (that is, the absolute value of the twist angle is equal to that of the display cell due to reverse twist) and Δn · d is 0.9 μm,
As shown in the figure, the spectrum in the off state is
It becomes almost flat. However, other conditions at this time are that α1 and α2 in FIG. 2 are 45 degrees and β is 90 degrees, respectively. FIG. 7 is a graph obtained by plotting the spectrum shown in FIG. 6 on color coordinates. It can be seen that the color is almost white as compared with the conventional method shown in FIG. As shown in the above example, the condition of the compensation cell 20 for performing the inverse conversion of the display cell 10 as shown in FIG. 5 is present regardless of the wavelength. The correspondence function is as follows. That is, (1) The absolute value of Δn · d of the display cell is equal to the absolute value of Δn · d of the compensation cell.

(2) When the twist angle t1 of the display cell is θ, the twist angle t2 of the compensation cell is minus θ (the twist direction is opposite).

(3) The angle β between the rubbing direction R12 of the upper substrate of the display cell and the rubbing direction R21 of the lower substrate of the compensation cell is 90.
It is degree.

When the above three conditions are satisfied, the value of Δn · d and the twist angle
Irrespective of the values of t1 and t2, the coloring in the off state of the liquid crystal device can be completely eliminated, that is, whitening can be achieved.

The above description is all about the mechanism for eliminating the coloring in the off state. In the present invention, coloring in the ON state is also eliminated. It is not impossible to explain exactly the reason for eliminating the coloring in the ON state, but it is complicated. In any case, the inventor has experimentally confirmed that there is no or almost no on-state coloring even under various conditions, as shown in many practical examples in the following.

As described above, in order to completely eliminate the coloring in the off state of the positive mode, it is necessary to satisfy the above three conditions. However, in reality, as shown in FIG. 5, it is often practically sufficient that the compensation cell does not completely reverse the conversion of the display cell. This is conceptually shown in FIG. FIG. 8 corresponds to FIG. The difference from FIG. 5 is the state of each polarization after passing through the compensation cell 20 '.
This means that b3 ', g3', r3 'is slightly elliptically polarized light, not perfect linearly polarized light like b3, g3, r3 in FIG. As a result, the polarized light b4 ′ · g4 ′ after passing through the polarizing plate 2
-R4 'has a slight wavelength dependence in its intensity. Nevertheless, the appearance spectrum of the positive mode is almost white in the off state and almost black in the on state, and coloring may be almost completely eliminated on the color coordinates.

As described above, even if the above three conditions are not satisfied, there are practically conditions for the compensation cell that can sufficiently eliminate the coloring.

Alternatively, for other reasons, it may be preferable to use compensation cells other than the above three conditions in a positive sense. One of the reasons is that the characteristics of the polarizing plate generally have wavelength dependence. An example of this is shown in FIG. By appropriately selecting the conditions of the compensating cell for such wavelength characteristics, coloring as a liquid crystal device can be improved. This applies not only to the off state but also to the on state. Another reason is to change the condition of the compensation cell in consideration of the wide viewing angle.

The above description is for the state in which the transmittance in the off state is high, that is, the positive mode. Next, a description will be given of the state where the transmittance is low in the ON state, that is, the negative mode. If the orientation of the polarization axis of the polarizing plate 2 in FIG. 5 is set to be orthogonal to the polarization axis of the polarizing plate 1, none of the polarized lights b3, g3, r3, etc. can pass through the polarizing plate 2. Therefore, the spectrum of the transmitted light at this time coincides with the spectrum of the polarizing plate in the crossed Nicols state shown in FIG. 3 II (however, the light absorption in the liquid crystal cell and the compensation cell etc. is neglected). This state is the darkest state that can be obtained using the polarizing plate shown in FIG. As described above, according to the present invention, the desired flat spectral characteristic can be obtained even in the negative mode by using the compensation cell.
That is, coloring can be eliminated in any case.

It should be noted that the following description will be given on the positive mode.

Next, the outline of a specific method for calculating the change in the polarization state of light that has passed through the compensation cell will be described below.

Light incident on the compensation cell is generally elliptically polarized. The reference plane trace of elliptically polarized light that advances in the positive direction of the Z axis can be expressed as follows by a column vector having xy components as elements.

Where a _x and a _y are the amplitudes of the xy components, ω is the angular frequency,
ψ _x · ψ _y indicates the phase angle of the xy component. But in this case
Since the absolute phase of the wave is not a problem, the optical frequency and absolute phase terms of equation (6) were omitted, and the polarization state was described by the normalized Jones vector of the following equation, which also normalized the amplitude of each component.

Now, the polarized light E of the formula (7) passes through the compensation cell and its polarization state is changed to be polarized light E ′. Compensation cells are represented by a 2x2 Jones matrix that performs this transformation.

For example, when this compensation cell (optically anisotropic body) is a uniaxial positive linear retarder like a film polymer, the Jones matrix R _{Δ · θ} can be expressed by the following equation.

Where θ is an angle formed by the fast axis of the linear phaser and the X axis,
Δ indicates retardation. It should be noted that the retardation Δ is calculated by using Δn · d of the linear retarder and the wavelength λ of light, and
It is defined by ≡2πΔn · d / λ.

From the left side of the incident light vector E, the polarization state of the light that has passed through this film polymer is calculated from the Jones matrix R of equation (8).
_{The value is calculated} by the following equation by _{applying Δ · θ} .

E ′ = R _{Δ · θ} E If the compensation cell is formed by stacking a plurality of film polymers, from the left side of the incident light vector E,
According to the order in which light passes, the Jones matrix of equation (8) is sequentially applied to obtain the following equation.

E ′ = R _{Δn · θn} R _{Δn-1 · θn-1} ... R
_{The Δ2θ2} R _{Δ1 · θ1} E compensation cell is complicated as a retarder because the liquid crystal molecules are twisted and aligned. However, FIG. 9 (a)
If the liquid crystal layer is divided into a sufficiently large number of layers as described above, it can be approximated by stacking liquid crystal layers that are not twisted and oriented as shown in FIG. 9 (b). Since the liquid crystal layer not twist-aligned is a uniaxial linear retarder, which is the same as the film-like polymer, the polarization of the light passing through the compensation cell is performed in the same manner as in the case where a plurality of the film-like polymers are stacked. You can ask for status.

Using the method described above, the angle t1 in FIG. 2 is set to 200 degrees,
Angle t2 is minus 200 degrees, angle α1 is 45 degrees, angle α2 is 4
5 degree, 90 degree angle β, Δn
Under the above-mentioned conditions, where d is 0.9 μm, the transition of the polarization state of light calculated by dividing the liquid crystal layer into 20 parts,
It is shown in FIGS. 10 to 12. FIG. 10, FIG. 11 and FIG. 12 show polarization state transitions of light having wavelengths of 450 nm, 550 nm and 650 nm, respectively. For example, in the case of FIG. 10, linearly polarized light b11 incident on the display cell in FIG. 10 (a) changes its polarization state to b12, b13, and b14 after passing through five layers, and exits the cell with elliptical polarization of b15. . This elliptically polarized light b15 is subsequently incident on the compensation cell in the same figure (b), and the polarization state transits to b16, b17, b18 again after passing through five layers, and is emitted from the compensation cell as linearly polarized light of b19. In each of the above steps, the polarization state conversion by the compensation cell of FIG.
This is equivalent to the inverse conversion of the conversion by the display cell, and therefore, the light incident on the display cell exits the compensation cell in exactly the same polarization state. As is clear from FIGS. 11 and 12, this effect exists regardless of the wavelength of light, so in the liquid crystal device having the configuration of the present invention, coloring in the off state is completely eliminated and whitening occurs. It will be possible.

Further, as described above, the second type of the compensating cell or the like which is an optically anisotropic body capable of sufficiently eliminating the coloring without satisfying the above three conditions.
The conditions for the nematic liquid crystal layer exist. The conditions are
Light incident on one of the polarizing plates becomes elliptically polarized light having a different major axis direction for each wavelength between the display cell and the second nematic liquid crystal layer adjacent to the display cell, and then enters the other polarizing plate. In this case, the second nematic liquid crystal layer may be arranged so as to be elliptically polarized light in which the major axis direction is substantially uniform for each wavelength. Hereinafter, this is called the NTN condition. Specifically, the twist angle and Δn · d of the liquid crystal layer of the compensation cell or the like are appropriately set according to the twist angle of the display cell and the value of Δn · d. The condition will be described below based on a specific example.

Concrete Example 1 In FIGS. 1 and 2, the twist angle t1 of the liquid crystal of the display cell is twisted to the left by about 200 degrees, Δn · d is about 0.9 μm, the angle β is about 90 degrees, and the angles α1 and α2 are respectively. When the range is from 30 to 60 degrees, the twist angle t2 and Δn of the liquid crystal in the compensation cell are
When d is the shaded portion in FIG. 13, a liquid crystal device is obtained which becomes almost white in the off state and almost black in the on state.

The above conditions can be obtained by calculation using the equations (6) to (8), and an example of the calculation method will be described below.

That is, the liquid crystal of the display cell of Δn · d = 0.9μm that is twisted 200 ° to the left is divided into 200 in the cell thickness direction, and a uniaxial retarder of Δn · d = 0.0045μm per layer is left. The calculation is performed according to the above formula assuming that the structure is twisted by 1 °. The wavelength of light used at this time is 400 nm to 7
It is in the range of 00 nm. The polarization state of the light incident on the liquid crystal of the display cell differs depending on the type of polarizing plate used and the axial direction, but here the ideal polarizing plate (transmissivity at parallel Nicols 50%
%, Transmittance at crossed Nicols 0%). The angle α1 formed by the rubbing direction of the substrate adjacent to the polarizing plate (direction of liquid crystal molecules on the substrate surface) and the direction of the polarizing axis of the polarizing plate is set to 45 °. Then, the linearly polarized light that has passed through the polarizing plate enters the display cell, and the state of elliptically polarized light of each wavelength that has passed through the display cell is obtained.

Next, the state of the elliptically polarized light after the elliptically polarized light enters and passes through the compensation cell is obtained. The elliptically polarized light incident on the compensation cell is obtained by the same calculation as above, and the angle β formed by the rubbing directions of the adjacent substrates of the compensation cell and the display cell is 90 degrees. In addition, the liquid crystal of the compensation cell is divided into 200 in the thickness direction of the cell, and the uniaxial retarder is twisted by 0.7 degrees to the right and twisted by 140 degrees to the right as a whole.
When n · d is an appropriate value, the state of elliptically polarized light that has passed through the compensation cell can be obtained from the above calculation formula. Further, the angle α2 formed by the rubbing direction of the substrate adjacent to the polarizing plate and the direction of the polarizing axis of the polarizing plate is set to 45 degrees, the spectrum after passing through the polarizing plate is obtained, and the Y value after the luminosity correction is obtained.

In the above calculation, assuming that the value of Δn · d of the liquid crystal of the compensation cell is from 0 μm to 1.5 μm, the relationship between Δn · d of the compensation cell and the Y value after the visibility correction is obtained. At this time, when Δn · d of the compensation cell is plotted on the horizontal axis and the Y value is plotted on the vertical axis, the Y value has a maximum value and a minimum value and changes periodically as shown in FIG. Since there are two directions in which the angle formed by the polarization axis and the rubbing direction is 45 degrees, two curves are drawn in FIG. 14 described above.

Display modes include a negative mode (dark when no voltage is applied) and a positive mode (bright when no voltage is applied). In the negative mode, it is desirable that the no-voltage application state is darker, and in the positive mode, the no-voltage application state is brighter. Therefore, in FIG. 14, the portion having the maximum Y value is suitable for the positive mode, and the portion having the minimum Y value is suitable for the negative mode.

The Y value in the voltage application state in the conventional negative mode is as high as about 5%, and it can be seen that it is clearly colored in blue both visually and on the color coordinates.

On the other hand, the minimum Y value in FIG. 14 is less than half the Y value in the negative mode of the conventional STN type liquid crystal device. The color at this time is slightly colored on the color coordinates, but the Y value is small, so it is visually recognized as a color sufficiently close to black.
It is recognized as white when a voltage is applied. Therefore, in the negative mode, black-and-white display can be obtained in the area where the Y value is the minimum, and at this time, Δn · d is the desired value.

The portion where the Y value is maximum becomes closer to white in visual observation and in color coordinates, as compared with the color in the state where no voltage is applied in the conventional positive mode. However, it is close to white even before and after the portion where the Y value is maximum. Therefore, in the positive mode, a black and white display can be obtained in a fairly wide range, and it is very difficult to judge the boundary. Further, since the angle formed by the polarization axis and the rubbing direction is 45 degrees, when the direction of the polarization axis in the case of the one curve in FIG. 14 is shifted by 90 degrees, it coincides with the polarization axis of the other curve. Therefore, the maximum and minimum values of Δn · d in FIG. 14 are the same.

From the above, black and white means that the Y value is minimum Δn
d. In other words, if the display cell has a left twist of 200 degrees, Δn
・ When d = 0.9 μm, the angle α1 formed by the rubbing direction of the substrate of the display cell adjacent to the polarizing plate and the direction of the polarization axis of the polarizing plate is 45 degrees, and the rubbing of each of the substrates adjacent to the display cell and the compensation cell is performed. The angle β formed by the directions is 90 degrees, the compensation cell is twisted to the right by 140 degrees, and the angle α2 formed by the rubbing direction of the substrate of the compensation cell adjacent to the polarizing plate and the polarization axis direction of the polarizing plate is 45 degrees. Sometimes Δn · d of the compensation cell is 0.33
μm, 0.7 μm, 1.0 μm, 1.3 μm (Δn
A black and white display is obtained when d is 1.5 μm or less) (see FIG. 14).

Next, when the rubbing direction of the substrate of each cell adjacent to the polarizing plate and the polarization axis directions α1 and α2 of the polarizing plate are other than 45 degrees,
Calculations are performed in the same procedure when the angle formed by the rubbing directions of the adjacent substrates of the display cell and the compensation cell is other than 90 degrees. Then, Δn · d of the compensation cell having the minimum Y value is obtained as a range having a certain width and periodically appearing (in FIG. 13, the distribution of Δn · d when the twist angle is fixed at 140 degrees to the right). However, the angle formed by the directions of the respective axes at this time is within a range in which the minimum Y value is 3% or less, or there is no extreme coloring.

Also, when the condition of the display cell is left as it is and only the magnitude of the twist angle of the compensation cell is changed, the range of Δn · d of the compensation cell where the Y value becomes the minimum appears periodically as in the above case. . FIG. 13 summarizes the relationship between the magnitude of the twist angle of the compensation cell and Δn · d obtained in this way. That is, from FIG. 13, when the display cell is twisted to the left by 200 degrees and Δn · d is 0.9 μm, there is only one condition of Δn · d and the size of the twist angle of the compensating cell that can obtain a monochrome display. Rather, it can be seen that certain fan-shaped ranges exist periodically.

Further, even when the twist angle magnitude and Δn · d of the display cell are changed, the twist angle magnitude and Δn · d of the compensating cell for obtaining a monochrome display can be obtained by the same procedure as above. Also in this case, the twist angle of the compensation cell and Δn ·
The relationship of d is fan-shaped and appears periodically.

In this way, for the twist angle and Δn · d of an arbitrary display cell, the twist angle and Δ of the compensation cell for displaying in black and white
It is possible to obtain n · d, and the twist angle and Δn · d of the compensating cell are not unique, and there are many.

Example 2 In Example 1, the angle α2 in FIG. 2 is about 40 degrees, the liquid crystal twist angle t2 of the compensation cell is about 140 degrees right twist, the angle β is about 90 degrees, and the liquid crystal twist angle t1 of the display cell is about 90 degrees. Is a left twist of about 200 degrees, the angle α1 is about 40 degrees, and Δn · d of the liquid crystal layer of the compensation cell is
Is about 0.7 μm, and Δn · d of the liquid crystal layer of the display cell is about 0.9 μm
And The appearance spectrum of the liquid crystal device at this time is
Shown in the figure. In the figure, curve I shows the off state, and curve II shows the on state. The spectrum of the appearance of the conventional liquid crystal device shown in FIG. 31 is yellow when off (curve I) and blue when on (curve II). However, as shown in FIG. 15, in the liquid crystal device of the present invention, it is almost white in the off state and almost black in the on state.

Specific Example 3 In Specific Example 1, the angle α2 in FIG. 2 is about 40 degrees, the twist angle t2 of the liquid crystal in the compensation cell is right twist of about 200 degrees, the angle β is about 90 degrees, and the twist angle t1 of the liquid crystal of the display cell is t1. Is left twist of about 200 degrees, angle α1 is about 50 degrees, Δn · d of the liquid crystal layer of the compensation cell
Is about 0.9 μm, and Δn · d of the liquid crystal layer of the display cell is about 0.9 μm
And The appearance spectrum of the liquid crystal device at this time is
Shown in the figure. In the figure, curve I shows the off state, and curve II shows the on state. In this case also, as in Example 2,
It is almost white in the off state and almost black in the on state.

Concrete Example 4 In Concrete Example 1, the angle α2 in FIG. 2 is about 40 degrees, the twist angle t2 of the liquid crystal in the compensation cell is right twist of about 260 degrees, the angle β is about 90 degrees, and the twist angle t1 of the liquid crystal in the display cell is t1. Is a left twist of about 200 degrees, the angle α1 is about 40 degrees, and Δn · d of the liquid crystal layer of the compensation cell is
Is about 0.8 μm, and Δn · d of the liquid crystal layer of the display cell is about 0.9 μm
And The appearance spectrum of the liquid crystal device at this time is
Shown in the figure. In the figure, curve I shows the off state, and curve II shows the on state. Also in this case, as in the second and third examples, the white state is almost white in the off state and the black state is almost in the on state.

Example 5 In FIG. 2, the twist angle t1 of the liquid crystal of the display cell is about 250.
Left twist, Δn · d is about 0.9 μm, angle β is about 90
If the degrees and angles α1 and α2 are in the range of 30 to 60 degrees, respectively, the twist angle t2 and Δn · d of the liquid crystal of the compensation cell are
A liquid crystal device having a white color in the off state and a substantially black color in the on state can be obtained when the shaded portion in FIG. 18 is used.

Example 6 In Example 5, the angle α2 in FIG. 2 is about 40 degrees, the twist angle t2 of the liquid crystal in the compensation cell is right twist of about 160 degrees, the angle β is about 90 degrees, and the twist angle t1 of the liquid crystal in the display cell is t1. Is a left twist of about 250 degrees, the angle α1 is about 40 degrees, and Δn · d of the liquid crystal layer of the compensation cell is
Is about 0.8 μm, and Δn · d of the liquid crystal layer of the display cell is about 0.9 μm
And The spectrum of the appearance of the liquid crystal device at this time is
Shown in the figure. In the figure, curve I shows the off state, and curve II shows the on state. In this case also, as in Example 2,
It is almost white in the off state and almost black in the on state.

Example 7 In FIG. 2, the angle α2 is about 40 degrees, the liquid crystal twist angle t2 of the compensation cell is right twist of about 360 degrees, the angle β is about 90 degrees, and the liquid crystal twist angle t1 of the display cell is about 250 degrees. Left twist, the angle α1 is set to about 40 degrees, and Δn · d of the liquid crystal layer of the compensation cell
Is about 1.0 μm, and Δn · d of the liquid crystal layer of the display cell is about 0.9 μm
And At this time, the liquid crystal device becomes white in the off state and more black in the on state.

Example 8 In FIG. 2, the angle α2 is about 50 degrees, the liquid crystal twist angle t2 of the compensation cell is about 170 degrees right twist, the angle β is about 90 degree, and the liquid crystal twist angle t1 of the display cell is about 170 degree. Left twist, the angle α1 is set to about 40 degrees, and Δn · d of the liquid crystal layer of the compensation cell
Is about 0.7 μm, and Δn · d of the liquid crystal layer of the display cell is about 0.7 μm
And At this time, the liquid crystal device becomes white in the off state and becomes blacker in the on state.

Concrete Example 9 In FIG. 2, the twist angle t1 of the liquid crystal of the display cell is about 120.
Left twist, Δn · d is about 0.9 μm, angle β is about 90
If the degrees and angles α1 and α2 are in the range of 30 to 60 degrees, respectively, the twist angle t2 and Δn · d of the liquid crystal of the compensation cell are
When the shaded area in FIG. 20 is used, a liquid crystal device is obtained in which the liquid crystal device becomes almost white in the off state and almost black in the on state.

Example 10 In FIG. 2, the twist angle t1 of the liquid crystal of the display cell is about 200.
Left twist, Δn · d is about 0.6 μm, angle β is about 90
If the degrees and angles α1 and α2 are in the range of 30 to 60 degrees, respectively, the twist angle t2 and Δn · d of the liquid crystal of the compensation cell are
When the shaded portion in FIG. 21 is used, a liquid crystal device is obtained in which the liquid crystal device becomes almost white in the off state and almost black in the on state.

Concrete Example 11 In FIG. 2, the twist angle t1 of the liquid crystal of the display cell is about 200.
Left twist of degree, Δn · d about 1.5 μm, angle β about 90
If the degrees and angles α1 and α2 are in the range of 30 to 60 degrees, respectively, the twist angle t2 and Δn · d of the liquid crystal of the compensation cell are
When the shaded portion in FIG. 22 is used, a liquid crystal device is obtained in which it is almost white in the off state and almost black in the on state.

Example 12 In FIG. 2, the twist angle t1 of the liquid crystal of the display cell is about 350.
Left twist, Δn · d is about 0.9 μm, angle β is about 90
If the degrees and angles α1 and α2 are in the range of 30 to 60 degrees, respectively, the twist angle t2 and Δn · d of the liquid crystal of the compensation cell are
When the hatched portion in FIG. 23 is used, a liquid crystal device is obtained in which the liquid crystal device is almost white in the off state and almost black in the on state.

The above specific examples 1 to 12 are examples of the NTN conditions.

In the present invention, the liquid crystal layer such as the compensation cell 20 for the display cell 10 is set to the NTN condition as described above, and the temperature of the NI point of the first nematic liquid crystal, that is, the liquid crystal of the display cell is T ₁ (° K). When the temperature of the NI point of the second nematic liquid crystal, that is, the liquid crystal of the compensation cell is T ₂ (° K), a liquid crystal having 0.86 ≦ T ₂ / T ₁ ≦ 1.15 is used. By doing so, even if the Δn · d of the liquid crystal layer of the display cell and the compensation cell changes due to the temperature change, it is possible to minimize the change in the appearance color of the liquid crystal display device.

That is, when the NTN conditions as described above are set, both cells 10
If the magnitude of Δn · d of 20 deviates, the black level in the off state in the negative mode deteriorates, and the contrast also decreases. As an example, a case will be described in which the display cell has a left twist of 240 ° and Δn · d = 0.9μ, and the compensation cell has a right twist of 240 ° and Δn · d = 0.9μ. No. 2
Figure 4 shows the changes in transmittance and contrast when the compensation cell and display cell deviate in Δn · d. The horizontal axis in the figure shows the ratio of compensation cell and display cell Δn · d, and the left vertical axis. Is the transmittance (%) when no voltage is applied, and the vertical axis on the right is the contrast. As can be seen from the figure, when Δn · d shifts, the transmittance becomes high and the contrast becomes low. When Δn · d is the set value, the transmittance is 0.2% or less and the contrast 24 is obtained. A contrast of 10 can be obtained even if Δn · d is shifted and the transmittance becomes about 1.0%. Fig. 25 shows the chromaticity diagram at this time. In the figure, Δn
The color when the ratio of d is 1.00 is shown in I, and the color when the ratio of 0.94 and 1.06 (when the transmittance is about 1.0%) is shown in II. In FIG. 25, both I and II are colored in terms of color purity, but the transmittance is low (II
However, since the transmittance is 1%), it can be judged to be sufficiently black. That is, if the transmittance is 1% or less, sufficient black and white display can be obtained. From this, the compensation cell and display cell Δn
The ratio of d may be set in the range of 0.94 to 1.06 (condition for obtaining a contrast of 1:10 or more in black and white).

The NI point of a liquid crystal is the temperature at which the phase transitions from the nematic state to the isotropic state. As shown in FIG. 26, the refractive index anisotropy Δn of liquid crystal has a temperature dependence that decreases with an increase in temperature. Therefore, if Δn · d is set using Δn at 20 ° C, Δn · d will deviate from the set value when the temperature is other than 20 ° C. If the same liquid crystal is used for the compensation cell and the display cell (the components other than the optical activator are the same), the Δn of the liquid crystal of the compensation cell and that of the display cell will change the same even if the temperature changes. The ratio of d does not change. However, when different liquid crystals are used for the compensation cell and the display cell, the rate of change of Δn with temperature is different, so the ratio of Δn · d between the compensation cell and the display cell at 20 ° C (also referred to as the ratio of Δn). Even if is set to 1.0, the ratio of Δn · d between the compensation cell and the display cell becomes a value other than 1.0 except at 20 ° C. When the ratio of Δn · d between the compensation cell and the display cell is in the range of 0.94 to 1.06 within the operating temperature range of the cell, sufficient display can be obtained as described above.

Generally, the magnitude of the temperature dependence of Δn is related to the height of the NI point of the liquid crystal. When the operating temperature range is from 0 ° C to 40 ° C, the higher the NI point, the smaller the Δn ratio (change amount) of the liquid crystal at 0 ° C and 40 ° C. For example, a liquid crystal with an NI point of 96 ° C
Even if Δn is 0.171 at 20 ℃, it becomes 0.178 at 0 ℃ and 0 at 40 ℃.
Change with 160. Also, the liquid crystal with an NI point of 55 ° C has Δn at 20 ° C.
Even at 0.171, the amount of change is 0.186 at 0 ° C and 0.137 at 40 ° C. This means that the ratio of Δn of liquid crystals with different NI points is 0.957 at 9 ° C even if it is 1.0 at 20 ° C.
It becomes 1.168 at 40 ℃. Since the cell thickness does not change depending on the temperature, the ratio of Δn directly becomes the ratio of Δn · d.
If these two liquid crystals are used for the compensation cell and the display cell, respectively, the twist angle, Δn
・ Even if d is set, the value of Δn changes at 0 ° C or 40 ° C, so it deviates from the NTN condition.

Here, the temperature T ₁ at the NI point of the liquid crystal of the display cell is 60 ° C, 100
The temperature T ₂ of the NI point of the liquid crystal of the compensation cell is calculated so that the ratio of Δn between the liquid crystal of the compensation cell and the display cell is 0.94 to 1.06 in the temperature range of 0 ° C to 40 ° C. It shows in Table 1. At this time, Δn of the liquid crystal of the compensation cell and the display cell
The ratio should be set to 1.0 at 20 ° C. The temperature dependence of Δn was obtained by standardizing the temperature dependence of three kinds of liquid crystals.

As shown in Table 1 above, for example, if the temperature T _{1 at} the NI point of the liquid crystal of the display cell is 60 ° C., assuming Δn ₁ at 20 ° C. to be 1.0, a change of 1.10 at 0 ° C. and 0.90 at 40 ° C. To do. When the operating temperature range is 0 ° C to 40 ° C, the liquid crystal NI of the compensation cell
Since sufficient display characteristics of temperature T ₂ in non When 40 ° C. over 50 ° C. of the point can not be obtained, the temperature T ₂ of the liquid crystal of the NI point of the compensation cell 50
℃ or more is required. For a liquid crystal having T ₂ of 50 ° C., Δn ₂ at 20 ° C. is 1.01 at 0 ° C. and 0.89 at 40 ° C. That is, the ratio of Δn ₁ of the liquid crystal of the display cell to Δn ₂ of the liquid crystal of the compensation cell is 1.01 at 0 ° C and 0.99 at 40 ° C, which is 0.94.
It is within the range of 1.06.

Next, consider the case where the temperature T _{2 at} the NI point of the liquid crystal of the compensation cell is high. When the temperature T _{2 at} the NI point of the liquid crystal in the compensation cell is 110 ° C. or lower, the ratio of Δn between the liquid crystal in the display cell and the compensation cell in the range from 0 ° C. to 40 ° C. falls within the range from 0.94 to 1.06. When the temperature T ₁ at the NI point of the liquid crystal of the display cell is 100 ° C, 0
When the temperature T _{2 at} the NI point of the compensation cell is 50 ° C. or higher, the ratio of Δn between the liquid crystal of the display cell and the compensation cell in the range of 40 ° C. is 0.94 to 1.06. Even 190 ° C. The T ₂ are the case where a higher temperature of the liquid crystal of the NI point of the compensation cell from the display cell, the ratio of the liquid crystal of Δn of the display cell and the compensation cell from 0.96 1.
It is as small as 04. Similarly, when the temperature T ₁ of the NI point of the liquid crystal of the display cell is 130 ° C., the NI point of the liquid crystal of the compensation cell may be set in the range of 65 ° C. to 190 ° C. The above range is shown in FIG.

In FIG. 27, the horizontal axis represents the temperature T _{1 at} the NI point of the display cell, and the vertical axis represents the temperature T ₂ at the NI point of the compensation cell. In the figure, the alternate long and short dash line shows the case where the temperatures of the NI points of the liquid crystal of the compensation cell and the display cell are equal. The solid line arrow in the figure is in the range of 0 ° C to 40 ° C, the ratio of the liquid crystal Δn of the compensating cell to the display cell is in the range of 0.96 to 1.04, and the broken line arrow is in the range of 0 ° C to 40 ° C. The range in which the ratio of Δn of the liquid crystal of the cell and the display cell is from 0.94 to 1.06 is shown. The temperature of the NI point of the liquid crystal of the compensation cell and the temperature of the liquid crystal of the display cell may be within the range indicated by the broken line arrow, but it is needless to say that the temperature is the same. In terms of cost and ease of making, it is desirable to set the range within the shaded area. If this range is expressed by an equation, Ie And when expressed in absolute temperature, That is, as mentioned above It will be.

By setting the conditions as described above, it is possible to reduce as much as possible the change in the appearance color of the liquid crystal display device even if the Δn · d of the liquid crystal layer of the display cell and the compensation cell changes due to the temperature change. .

In the above embodiment, the same effect can be obtained by arranging the compensation cell and the display cell upside down. Further, the same effect can be obtained by replacing the two substrates of the compensation cell lower substrate 21 and the display cell upper electrode substrate 12 shown in FIG. 1 with one substrate.

FIG. 24 shows the display cell 10 between the upper and lower polarizing plates 2 and 1.
An example in which the compensation cells 20 and 30 are provided on the upper and lower sides of the above is shown. For example, the liquid crystal molecules of the upper compensation cell 20 and the lower compensation cell 30 are both twisted to the right, and the liquid crystal molecules of the display cell 10 are twisted to the left. The sum of the twist angle of the liquid crystal molecules of the upper compensation cell 20 and the twist angle of the liquid crystal molecules of the lower compensation cell 30 at this time is taken as the twist angle of the entire compensation cell, and Δn · d of the liquid crystal layer of the upper compensation cell 20 is The sum of Δn · d of the liquid crystal layer of the lower compensation cell 30 is taken as Δn · d of the entire compensation cell. The twist angle of the entire compensation cell and Δn · d of the entire compensation cell are shown in the first specific example.
Even under the conditions described in Nos. 1 to 12, the same effects as in Examples 1 to 12 can be obtained. The same effect can be obtained by arbitrarily changing the arrangement order of the cells 10, 20 and 30. Further, the compensation cell may be provided in three layers or more under the same conditions as above.

Further, in the above structure, the lower substrate 21 of the upper compensation cell 20 is
And two substrates of the upper electrode substrate 12 of the display cell 10 are replaced with one substrate. Furthermore, the two substrates of the lower electrode substrate 11 of the display cell 10 and the upper substrate 32 of the lower compensation cell 30 are replaced with one substrate. In this way, the number of substrates is reduced, the structure is simplified, and the same effect as the above case can be obtained.

Furthermore, in the above examples, when a liquid crystal having a positive dielectric anisotropy Δε is used as the liquid crystal of the compensation cell, the alignment of the liquid crystal of the compensation cell is disturbed by the influence of external static electricity, and the appearance of the liquid crystal display device is colored. Unevenness may appear. Therefore, if a liquid crystal having a negative dielectric anisotropy Δε is used as the liquid crystal of the compensation cell, a liquid crystal device in which appearance color unevenness does not occur even if there is an external static electricity effect is obtained. However, electrodes are attached inside the upper and lower substrates of the compensation cell, and the liquid crystal of the compensation cell having a positive Δε is used. By doing so, even if the appearance color of the liquid crystal display device changes due to temperature change, it is possible to cancel the color change by applying a voltage between the electrodes attached to the upper and lower substrates of the compensation cell. .

Further, the compensation cell and the display cell may be optically adhered to each other in order to prevent reflection of light on the substrate surface where the compensation cell and the display cell are in contact with each other. The polyvinyl butyral film that has been embossed is used as the adhesive layer and is adhered by heating and pressing. Alternatively, a heat-effect epoxy-based or urethane-based adhesive may be used as the adhesive. Further, an acrylic ultraviolet adhesive may be used. By adhering the compensation cell and the display cell as described above, it is possible to reduce reflection at the boundary surface between the two cells.

Further, by placing the reflection plate on the outer side of either the upper or lower polarizing plate, a reflection type liquid crystal device can be obtained.

〔The invention's effect〕

As described above, the present invention can solve the coloring phenomenon, which is a major drawback of the conventional STN type liquid crystal device. In other words, the present invention enables perfect black and white display. Not only that, but the amount of light in the transmitted state increased, resulting in a bright display. Furthermore, the amount of leak light in the non-transmissive state was extremely small, and the contrast ratio was greatly improved in combination with the increase in the amount of light in the transmissive state. Further, it has become possible to reduce as much as possible the change in the appearance color due to the change in Δn · d of the liquid crystal layer due to the temperature change.

Due to the above effects, the present invention can exhibit good color display characteristics when applied to color display, for example.
In particular, when the twist angle was 180 degrees or more, the clear view direction was the front, and the region near the front and near the concentric circle was the clear view region. For this reason, conventional TN
Wide viewing angle, viewing angle direction (oblique direction is oblique direction for TN type),
The contrast ratio has been greatly improved. Of course, the color display (8-color display) without gradation display is also improved compared to the TN type display.

Since the present invention can obtain the above effect regardless of the thickness of the liquid crystal layer of the display cell, it is possible to easily realize a high-speed response liquid crystal device by decreasing the thickness of the liquid crystal layer of the display cell. This is because the response speed is approximately proportional to the square of the thickness of the liquid crystal layer.

Further, since the present invention is effective in improving the contrast ratio as described above, it is also effective in improving the number of driving lines for multiplex driving.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a liquid crystal device according to an embodiment of the present invention. FIG. 2 is an explanatory view showing the relationship of each axis of the liquid crystal device. FIG. 3 is a diagram showing the wavelength dependence of the light transmittance of two polarizing plates used in a specific example of the present invention. FIG. 4 is a diagram showing an example of a driving method of the liquid crystal device of the present invention. FIG. 5 is a diagram showing the optical characteristics of the liquid crystal device according to the present invention in the off state. FIG. 6 is a diagram showing a spectrum of an off state of the liquid crystal device according to the present invention. FIG. 7 is an xy chromaticity diagram in which the spectrum of FIG. 6 is plotted on color coordinates. FIG. 8 is a diagram conceptually showing the case where the compensation cell is not the complete inverse conversion of the conversion of the display cell. FIG. 9A is a diagram schematically illustrating a cross section when the liquid crystal layer is divided into 10. FIG. 9 (b) is a view conceptually showing the relationship between the liquid crystal layer thickness and the twist angle in FIG. 9 (a). FIG. 10 is a diagram showing changes in the polarization state of light with a wavelength of 450 nm calculated by dividing the liquid crystal layer into 20 parts. FIG. 11 is a diagram showing changes in the polarization state of light with a wavelength of 550 nm calculated by dividing the liquid crystal layer into 20 parts. FIG. 12 is a diagram showing changes in the polarization state of light having a wavelength of 650 nm calculated by dividing the liquid crystal layer into 20 parts. FIG. 13 is a diagram showing a desirable range of compensation cells with respect to display cells in the embodiment of the present invention. FIG. 14 shows Δn when the range of FIG. 13 is derived by calculation.
The figure which shows the relationship of Y value with respect to d. FIG. 15, FIG. 16, and FIG. 17 are views showing the relationship between the wavelength and the transmittance characteristic of the appearance of the liquid crystal device according to the embodiment of the present invention. FIG. 18 is a diagram showing a desirable range of the compensation cell with respect to the display cell in the embodiment of the present invention. FIG. 19 is a diagram showing the relationship between the wavelength and the transmittance characteristic of the appearance of a liquid crystal device according to an example of the present invention. FIG. 20, FIG. 21, FIG. 22, and FIG. 23 are diagrams showing a desirable range of the compensation cell with respect to the display cell in the embodiment of the present invention. FIG. 24 is a diagram showing changes in transmittance and contrast when Δn · d of the display cell and the compensation cell are deviated. FIG. 25 is a chromaticity diagram when Δn · d of the display cell and the compensation cell are deviated. FIG. 26 is a diagram showing the relationship between the refractive index anisotropy of liquid crystal and temperature. FIG. 27 is a diagram showing the temperature range of the preferred NI point of the liquid crystal of the display cell and the compensation cell. FIG. 28 is a view showing the structure of a liquid crystal device of another embodiment of the present invention. FIG. 29 is a schematic view of a conventional super twisted nematic liquid crystal device. FIG. 30 is a diagram showing the relationship between the liquid crystal cell of the liquid crystal device and the polarization axis (absorption axis) of the polarizing plate. FIG. 31 is a diagram showing spectra of light transmittance of a pixel in an on state and a pixel in an off state during multiplex driving of a conventional liquid crystal device. Figure 32 shows the xy plotting the spectral curve in color coordinates.
Chromaticity diagram. FIG. 33 is a diagram showing optical characteristics of the above conventional liquid crystal device in an off state. 1 and 2 are polarizing plates, 10 is a display cell, 20 is a compensation cell, t1 and t2
Is the twist angle.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mitsuo Nagata 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Co., Ltd. (72) Inventor Kazuo Aoki 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Incorporated (56) References JP-A 64-519 (JP, A)

Claims (6)

[Claims] 1. A display cell in which a first nematic liquid crystal layer twisted and oriented at 120 ° or more is sandwiched between a pair of substrates having electrodes formed on opposing inner surfaces, and at least one optically anisotropic body. And a second nematic liquid crystal layer between the pair of polarizing plates, and the polarization axis direction of each polarizing plate is defined by the major axis direction of the liquid crystal molecules of the display cell or the second nematic liquid crystal layer adjacent to the polarizing plate. The light which is set in a predetermined direction except the direction substantially parallel or substantially orthogonal to and is incident on one of the polarizing plates is generated between the display cell and the second nematic liquid crystal layer adjacent to the display cell. The twist angle of the first nematic liquid crystal layer is such that elliptically polarized light having a different major axis direction for each wavelength becomes elliptically polarized light having a substantially uniform major axis direction for each wavelength when entering the other polarizing plate. And the second value depending on the value of Δn · d. Twist angle of the nematic liquid crystal layer and the Δ
The value of n · d is set to a predetermined value so as to eliminate the coloring of the display in the ON state and the OFF state of the display cell, and the temperature at the NI point of the first nematic liquid crystal layer is set to T ₁ (° K) and a temperature of the NI point of the second nematic liquid crystal layer is T ₂ (° K), a liquid crystal device using 0.86 ≦ T ₂ / T ₁ ≦ 1.15. 2. The angle between the polarization axis of at least one of the polarizing plates and the alignment direction of the liquid crystal molecules facing the one polarizing plate is 30 to 60 °. The liquid crystal device according to item 1). 3. A liquid crystal device according to claim 1, wherein a plurality of the second nematic liquid crystal layers are arranged. 4. The liquid crystal device according to claim 1, wherein the twisting directions of the first nematic liquid crystal layer and the second nematic liquid crystal layer are opposite to each other. 5. The first nematic liquid crystal layer and the second nematic liquid crystal layer.
3. The liquid crystal device according to claim 1, wherein the orientation direction of the liquid crystal molecules on the surface facing the nematic liquid crystal layer is approximately 90 °. 6. The twist angle and Δn · d of the first nematic liquid crystal layer and the second nematic liquid crystal layer are substantially the same, and the first (1) or (2). ) The liquid crystal device according to the item.