JPH0367219A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To improve the dependency of display characteristics on visual sensation by confining the product of the pitch of the spiral structure and refractive index of a cholesteric liquid crystal phase or high-polymer film to <=400nm. CONSTITUTION:The liquid crystal molecules of the cholesteric liquid crystal or chiral nematic liquid crystal exhibiting the cholesteric liquid crystal phase are oriented in approximately parallel with substrates 2, 5, 8 and a double refractive layer having the good characteristics is disposed between the convertional liquid crystal cell and polarizers 1, 9. The display element is so constituted that the product of the pitch of the spiral structure and refractive index of the cholesteric liquid crystal phase or the above-mentioned high-polymer film is <=400nm and the spiral axis of the spiral structure coincides approximately with the thickness direction of the double refractive layer. The dependency of the display characteristics on the visual sensation is decreased in this way and the liquid crystal display element having a high grade is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a liquid crystal display element.

[Prior Art and Problems to be Solved by the Invention] Liquid crystal display elements of a type that modulate light by changing the magnitude of birefringence of a liquid crystal layer by applying a voltage are already known. However, in this type of liquid crystal display element, the distance through which light actually passes through the liquid crystal layer changes depending on the viewing angle, and the magnitude of the apparent birefringence changes depending on the relative angle between the alignment direction of the liquid crystal molecules and the viewing angle direction. For this reason, the viewing angle dependence of the display characteristics is extremely large, and the angular range in which the display can be viewed is extremely small.

In order to reduce the viewing angle dependence of display characteristics,
It has been proposed to provide a birefringent layer between the liquid crystal layer and the polarizer. D that modulates light by changing the magnitude of refraction
It has been disclosed that in an AP type ECB type liquid crystal display element, a polymer film made to have negative optical anisotropy is provided as a birefringent layer, and viewing angle compensation is performed by the birefringent layer. Generally, the characteristics required of such a birefringent layer for viewing angle compensation are the mode (STN,
ECB, DAP, HAN, TB, etc.), cell parameters (optical axis direction of polarizer, birefringence size Δn of liquid crystal layer)
The in-plane refractive index is particularly effective for viewing angle compensation of AP, HAN, tilt alignment type, etc. liquid crystal display elements. nz,
A birefringent layer for viewing angle compensation in which ny is larger than the refractive index nz in the direction perpendicular to the surface has not been able to have good characteristics for the following reasons.

(2) - In an axially stretched polymer, the directions in which viewing angle can be compensated are limited to a narrow range because nz and ny are different.

■ Polymers such as those described in JP-A No. 62-210423 require very special molding.
It is difficult to make a homogeneous film, and it is also very difficult to control the magnitude of birefringence.

■ In a cell in which a general liquid crystal consisting of rod-shaped molecules is aligned, the refractive index n#tni in the long axis direction and short axis direction of the molecules is generally nz:>n, so homogeneous alignment is performed to obtain the above Although it is possible to create cells with similar characteristics, the range in which viewing angle compensation can be made is limited as described above.

The present invention has been made in view of the actual state of the prior art, and the present invention has been made in view of the actual state of the prior art.
) It is an object of the present invention to provide a high-quality liquid crystal display element in which viewing angle dependence of display characteristics is significantly reduced by using a homogeneous birefringent layer having a characteristic of nz.

[Means and operations for solving the problems] In order to achieve the above object, according to the present invention, there is provided a liquid crystal layer sandwiched between a pair of substrates having electrodes.

In a liquid crystal display element that is composed of a birefringent layer and a pair of polarizers arranged to sandwich these two layers from the outside, and modulates light by inputting an electrical signal to the electrodes, the birefringent layer is cholesteric. The pitch and refractive index of the helical structure of the cholesteric liquid crystal phase or the polymer film are composed of a liquid crystal compound exhibiting a liquid crystal phase or a polymer film obtained by fixing the orientation by rapid cooling of a cholesteric phase of a polymer. Provided is a liquid crystal display element characterized in that the product of the birefringent layer is 400 nm or less, and the helical axis of the helical structure substantially coincides with the thickness direction of the birefringent layer.

In the present invention, by aligning liquid crystal molecules of cholesteric liquid crystal or chiral nematic liquid crystal exhibiting a cholesteric liquid crystal phase approximately parallel to the substrate, a birefringent layer having the following characteristics ((i), (ii)) can be fabricated. By arranging the liquid crystal cell between the liquid crystal cell (hereinafter referred to as the "vibration cell") and the polarizer, the viewing angle dependence of the display characteristics of the liquid crystal display element is significantly reduced.

(i) In a plane, it can be considered to be approximately equidirectional with respect to visible light.

(n) The refractive index in the thickness direction is smaller than the average refractive index in the plane.

In order for a liquid crystal compound exhibiting a cholesteric liquid crystal phase aligned approximately parallel to the substrate (cholestic liquid crystal and chiral nematic liquid crystal, hereinafter the same) to satisfy the above characteristic (i), the size of the cholesteric pitch must be It is necessary that the product of the refractive index and the pitch of the liquid crystal be 400 nm to prevent coloring due to selective reflection due to the helical structure. Needs to be smaller.

The characteristic (if) above is satisfied whenever ordinary liquid crystal molecules are oriented substantially parallel to the substrate.

In addition, if a polymer is used that does not have a cholesteric phase at room temperature but takes a cholesteric phase with a product of pitch and refractive index smaller than 400 nm at higher temperatures than room temperature, it is possible to preserve the helical structure by rapid cooling from that temperature. , it can be used in the same manner as the above-mentioned liquid crystal compound exhibiting a cholesteric liquid crystal phase.

Next, the liquid crystal display element of the present invention will be explained in more detail with reference to the drawings.

The drawing is a sectional view showing a specific example of the structure of the liquid crystal display element according to the present invention, in which 1 and 9 are polarizers, 2°5.8 is a substrate, 3 and 6 are alignment films, and 4 and 7 are polarizers. is the sealing material, 10 is the first
A liquid crystal layer, 11 is a second liquid crystal layer, and 12 is an electrode.

The portion sandwiched between the daughter substrate 8 and the intermediate substrate 5 constitutes a driving liquid crystal cell, and the second liquid crystal layer 1 is aligned by an alignment film 6.
A voltage is applied to 1 using an electrode 12 to change the orientation state of the liquid crystal, thereby performing light modulation. The portion sandwiched between the upper substrate 2 and the intermediate substrate 5 constitutes a viewing angle compensation liquid crystal cell, and the liquid crystal molecules of the first liquid crystal layer 10 made of a liquid crystal compound exhibiting a cholesteric liquid crystal phase are approximately aligned with respect to the substrates due to the alignment film 3. oriented in parallel. According to the present invention, instead of a viewing angle compensation cell equipped with a liquid crystal layer made of a liquid crystal compound exhibiting a cholesteric liquid crystal phase, a polymer obtained by rapid cooling of a polymeric cholesteric phase can be used. The portions need not have a cellular configuration. Although a general horizontal alignment agent may be used to obtain a cholesteric phase composed of polymers oriented substantially parallel to the substrate, it is also possible to obtain a cholesteric phase by applying shear stress.

Typical examples of liquid crystal compounds exhibiting a cholesteric liquid crystal phase with a short pitch as used in the present invention include the following.

<Group ■> Tsuru H5 Yuin O Tsuru and H et al H5? CzHs and HCH, CH, GNP, c) I, and HC, H
.

?銚と■、 ３）Leots H2 This H5 Some of the substances included in the above Group I do not take a liquid crystal phase at room temperature, but they can be mixed with two or more substances in Group I, or with nematic liquid crystal. By mixing, it is possible to form a cholesteric phase at room temperature.

In addition, the following polypeptides and polyesters are representative of polymers that take a cholesteric phase with a short pitch at a temperature higher than room temperature and preserve the helical structure by rapid cooling.

<Group ■> (a) Copolymer of benzyl-L-glutamate and dodecyl-L-glutamate (b) 4,4'-dihydroxybiphenyl and (+)
Copolymer obtained by reaction of -3-methyladipic acid and aliphatic dicarboxylic acid The compounds used in the birefringent layer of the present invention are, of course, not limited to those exemplified above.

Furthermore, in the configuration example shown in FIG. 1, the intermediate substrate 5 is shared by the drive cell and the viewing angle compensation cell, but it is possible to make two liquid crystal cells completely separately using another substrate and then bond them together. is also possible. Furthermore, if the above-mentioned polymer is used instead of a viewing angle compensation cell equipped with a liquid crystal layer made of a liquid crystal compound exhibiting a cholesteric liquid crystal phase, the sealing material 4 etc. is not necessary, and the polymer oriented on one substrate can also be used. Can be used.

〔Example〕

Next, the present invention will be explained in detail.

Example 1 Vertical alignment agent FC-805 manufactured by 3M Co., Ltd. as an alignment agent
Using a spinner, this was applied to a glass substrate with a transparent electrode, baked, and then rubbed with a sponge. After scattering plastic beads having an average diameter of 11.0 - on this substrate, the two substrates were bonded together so that the rubbing directions were antiparallel to form a drive cell. ZLI-4318 (manufactured by Merck & Co., Ltd.), which is a nematic liquid crystal with negative induced anisotropy, was sealed in the g-motion cell.

On the other hand, as an alignment agent, horizontal alignment agent HL-l manufactured by Hitachi Chemical Co., Ltd.
A glass substrate without electrodes was coated with a spinner using llo, baked, and then rubbed with a sponge. Plastic beads having an average diameter of 40 pm were scattered on this substrate, and the two substrates were bonded together to form a viewing angle compensation cell. A liquid crystal represented by the following structural formula was sealed in this.

Since the temperature range in which this liquid crystal composition assumes a liquid crystal phase is 4 to 76°C, it can be treated as a single substance in the same manner as a general liquid crystal. This visual compensation cell is transparent and Il by polarized light microscopy.
It was found from observation that the helical axis was oriented almost perpendicularly to the substrate. A turbulence cell is sandwiched between two crossed nicol polarizing plates so that the rubbing direction is 45 degrees with respect to the transmission axis of the polarizing plate, and a driving signal is input to the electrodes. The color appeared. This color changes significantly depending on the viewing angle, and it has been found that the display characteristics are highly dependent on the viewing angle.When a viewing angle compensation cell was sandwiched between the primary turbulence cell and the polarizing plate, the viewing angle dependency of a single color change was reduced. We confirmed that the viewing angle was widened.

Example 2 Vertical alignment agent ZLI-3334 manufactured by Merck & Co., Ltd. as an alignment agent
A drive cell similar to that in Example 1 was manufactured using the following.

On the other hand, for viewing angle compensation, a polymer film prepared as follows was used instead of the cholesteric phase liquid crystal cell. In (b) of the above group ■, n=8, x:y=0
．． A small amount of 4:0.6 polymer was placed on a glass substrate, and 30
It was heated to about 0° C. and rolled between it and another glass substrate. Thereafter, the temperature was lowered to about 250° C. to form a cholesteric phase, and the two glass substrates were shifted until the entire sample became transparent.

This sample was then rapidly cooled. The thickness of the portion of the polymer sample not sandwiched between the two glass substrates was measured at several points and found to be approximately 45 pm.

When the polymer film prepared in this way was sandwiched between a drive cell and a polarizing plate, it was confirmed that the viewing angle dependence of display characteristics was reduced and the viewing angle was widened.

Example 3 Horizontal alignment agent HLIllo manufactured by Hitachi Chemical Co., Ltd. was placed on a glass substrate.
was applied to a thickness of about 1,000 coats, dried, and then rubbed in one direction with a sponge. A substrate that has been subjected to similar treatment and the above-mentioned substrate are placed 12 times apart so that the orientation treated surfaces face each other.
They were bonded together via a 4-diameter spacer. In the space between the peripheral boards, a cholesteric liquid crystal 7M736 manufactured by BDH
After injecting a cholesteric liquid crystal composition to which 15% by weight of cholesteric liquid crystal CBL5 manufactured by BDH was added, the liquid crystal was heated to 80°C to make the liquid crystal isotropic, and then cooled to room temperature to obtain a viewing angle compensation cell. T used in this example
The product of pitch and refractive index of M736 is 420nm, and blue coloring can be seen as it is, but by adding 15wt 2 of CB15, the product of pitch and refractive index becomes 360nm.
l++, and almost no coloring can be seen. The alignment of the liquid crystal is a nearly uniform domain, and when this liquid crystal cell was observed by sandwiching it between orthogonal polarizing plates, a nearly complete dark field was obtained. In addition, when we performed conoscopic observation using a polarizing microscope, a clear isogyr was observed at the center of the field of view, indicating that this liquid crystal cell can be optically regarded as a uniaxial crystal with its optical axis directed in the normal direction of the cell. It became clear. Further, when a sensitive color test plate was inserted during conoscope observation, an increase/decrease in retardation characteristic of negative uniaxial crystals was observed #A. Retardation of this liquid crystal cell (nx-nz)
- d (d is the thickness of the liquid crystal layer) was O, aps.

In addition, vertical alignment agent 005- manufactured by Chisso Corporation was applied on the glass substrate.
A 0.1$ solution of H was applied, heat treated at 120°C, and then rubbed in one direction with a sponge. A counter substrate that had been subjected to a similar treatment and the above substrate were pasted together through a spacer with a diameter of 6.4 μs so that the rubbing direction was antiparallel, and a Merck film with negative dielectric anisotropy was placed in the space between the peripheral substrates. Nematic liquid crystal ZLI4318 (Δn=
0.1243) to prepare an open cell.

Superimpose the parking cell and viewing angle compensation cell prepared above,
Furthermore, neutral gray polarizing plates are placed on the top and bottom,
A liquid crystal display element of the present invention was obtained. The upper and lower polarizing plates are arranged so that their transmission axes are perpendicular to each other and the rubbing direction of the rotating cell is 4.
They were arranged to form an angle of 5''.This liquid crystal display element is black when no voltage is applied, and has complete light-shielding performance.
It became white (transparent) when a voltage of about 3 V or more was applied.

Curve A in FIGS. 2 and 3 shows the viewing angle -
This shows the contrast characteristics. As is clear from these figures, the present liquid crystal display element was found to have an extremely wide viewing angle. Note that FIG. 2 shows the contrast for the front-back viewing angle, and FIG. 3 shows the contrast for the right-left viewing angle. In these figures, the horizontal axis is the angle from the cell normal.

(Comparative Example) In Example 3, a liquid crystal display element was constructed without using a viewing angle compensation cell. When viewed from the front, this liquid crystal display element was black when no voltage was applied and had a high light-shielding property, but when viewed from an angle, very noticeable light leakage occurred. As a result, the viewing angle-contrast characteristic has an extremely narrow viewing angle, as shown by curve B in FIGS. 2 and 3.

〔Effect of the invention〕

According to the present invention, it is possible to significantly improve the visual dependence of display characteristics by using a birefringent layer having good characteristics and manufactured by a simple method.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one configuration example of a liquid crystal display element according to the present invention, and FIGS. 2 and 3 are viewing angles (front-back and right-left) of each liquid crystal display element of Example 3 and Comparative Example. FIG. 3 is a diagram showing contrast characteristics. 1.9... Polarizer 2.5.8... Substrate 3.6... Alignment film 4.7... Seal material 10... First liquid crystal layer 11... Second liquid crystal layer 12 ···electrode

Claims (1)

[Claims] (1) Consists of a liquid crystal layer sandwiched between a pair of substrates having electrodes, a birefringent layer, and a pair of polarizers placed between these two layers from the outside, and transmits an electrical signal to the electrodes. In a liquid crystal display element that modulates light by inputting light, the birefringent layer is made of a liquid crystal compound exhibiting a cholesteric liquid crystal phase, or is made of a polymer film obtained by fixing the orientation by rapidly cooling the cholesteric phase of a polymer. , the product of the pitch and refractive index of the helical structure of the cholesteric liquid crystal phase or the polymer film is 400 nm or less, and the helical axis of the helical structure substantially coincides with the thickness direction of the birefringent layer. Characteristic liquid crystal display element.