JPH01205123A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To make the axially-symmetrical molecule orienting characteristic of a liquid crystal element utilizable by orienting liquid crystal molecules in such a way that on one substrate of the liquid cell the molecules are oriented with their major axes arranged in one direction and on the other substrate the molecules are oriented with their major axes arranged concentrically or radially. CONSTITUTION:After performing treatment so that liquid crystal molecules can be oriented homogeneously in one direction on the substrate 1 on the incident side and molecules can be oriented concentrically on the substrate 2 on the other side, liquid crystal 4 is enclosed into the liquid crystal cell formed of the base plates 1 and 2 with a spacer in between. When a linearly polarizing plate 5 is placed on the incident side, with the polarizing direction being made coincident with the oriented direction of the liquid crystal molecules, the polarizing direction of the light passed through the liquid crystal cell becomes the oriented direction of the molecules on the light emitting side, namely, concentric. On the other hand, when the polarizing direction of the polarizing plate 5 is turned to the direction perpendicular to the major-axis direction of the homogeneously-oriented liquid crystal molecules on the incident-side base plate 1, a radially polarized output is obtained. Therefore, an axially- symmetrical (centrally-symmetrical), such as concentric, radial, etc., polarizing characteristic can be obtained with a simple constitution.

Description

Detailed Description of the Invention [Industrial Applicability] The present invention relates to a liquid crystal element that utilizes axially symmetrical (centrosymmetric) polarization and molecular orientation characteristics, and the present invention relates to a liquid crystal element that utilizes axially symmetric (centrosymmetric) polarization and molecular orientation characteristics, and the present invention relates to a liquid crystal element that utilizes axially symmetric (centrosymmetric) polarization and molecular orientation characteristics. The present invention relates to improvements in alignment characteristics and viewing angle dependence of liquid crystal display elements.

[Prior art] A liquid crystal cell (homogeneously aligned liquid crystal) in which a field-effect liquid crystal with positive dielectric anisotropy is placed between two substrates with transparent electrodes, and the liquid crystal molecules are aligned parallel to the substrates. When a voltage higher than a threshold voltage is applied to the cell (cell), the force acting on the dipole moment of the liquid crystal molecules causes the liquid crystal molecules to change their orientation so that their long axes align with the direction of the electric field. Therefore, when the applied voltage is increased, the orientation of the liquid crystal molecules, which were oriented parallel to the substrate, can be continuously changed to the direction perpendicular to the substrate. Therefore, the apparent refractive index of the liquid crystal cell for incident light polarized in the orientation direction of the liquid crystal molecules changes continuously from a value for extraordinary light to a value for ordinary light. In a liquid crystal element whose liquid crystal layer is shaped like a lens, the apparent refractive index of the liquid crystal cell is changed by controlling the alignment direction of liquid crystal molecules using an applied voltage, thereby changing the focal length of the lens to a value for extraordinary light. It is already known in Japanese Unexamined Patent Publication No. 15854/1983 that the value can be changed continuously from 1 to 1 to the value for ordinary light. Note that if a vertically aligned liquid crystal with negative dielectric anisotropy is used, the change in focal length with respect to the applied voltage will be reversed. In addition, technical means for effectively reducing the thickness of the liquid crystal layer and improving response and recovery characteristics to applied voltage by forming the liquid crystal lens into a Fresnel lens structure have already been known, for example, from Japanese Patent Laid-Open No. 60-50510. However, in the molecular alignment method that aligns liquid crystal molecules in one direction,
There is a problem in that the alignment characteristics of liquid crystal molecules on a curved substrate may be locally non-uniform, and it is particularly difficult to obtain -like molecular alignment characteristics when the liquid crystal layer has a Fresnel structure. . By the way, in order to improve the molecular orientation characteristics of such a variable focal length lens using liquid crystal, technical means for orienting liquid crystal molecules axially symmetrically (centrosymmetrically), that is, concentrically or radially, within a liquid crystal cell has already been proposed. This method is known from JP-A-61-138922.

On the other hand, a liquid crystal device in which liquid crystal molecules are aligned in one direction on one glass substrate with a transparent conductive film attached, and perpendicular to that on the other substrate is a TN (twisted nematic). It is known as a liquid crystal, and is widely used as a display element that switches the state of light transmission by utilizing the effect of untwisting the crystal by applying a voltage. This TN liquid crystal has a so-called viewing angle dependency, in which visibility deteriorates in a certain specific direction.

In order to improve this viewing angle dependence, the liquid crystal molecules are arranged concentrically on one substrate and radially on the other substrate, that is, the liquid crystal molecules are oriented axially symmetrically (centrosymmetrically). There is a display element that exhibits the same transparent state switching effect as in the IEICE technical research report EID.
-86-14 (December 10, 1986). This axially symmetric (centrosymmetric) aligned liquid crystal cell has excellent visibility no matter which direction the display element is viewed from, except for a portion of the element, so it is particularly effective when viewing the display element from all around. It is.

[Problems to be Solved by the Invention] Incidentally, in order to operate a liquid crystal lens having molecular orientation characteristics of concentric circles, radials, or a combination thereof, it is necessary to use axially symmetric (centrosymmetric) polarized light as the incident light. must be used.

That is, a special polarizing plate exhibiting concentric or radial polarization characteristics is required. In order to make a variable focus lens without using such a special polarizing plate, the above-mentioned Japanese Patent Laid-Open No. 61.
As disclosed in Publication No.-138922,
Either a TN liquid crystal cell is sandwiched between two liquid crystal lenses with concentric alignment or radial alignment characteristics, and the TN liquid crystal cell is stacked on top of the other. It must have a structure in which liquid crystal cells with oriented liquid crystal molecules are superimposed.

On the other hand, it goes without saying that a polarizing plate having axially symmetrical (centrosymmetric) polarization characteristics is also required in a concentrically or radially oriented TN cell.

However, it is possible to create a polarizing plate with such axially symmetrical (centrosymmetric) characteristics by using a normal uniaxially stretched polymer film made of polyvinyl alcohol or the like and dichroic dye molecules such as iodine. This is extremely difficult.

By the way, there is a polarizing plate in which methylene blue molecules are oriented in one direction by applying a solution of methylene blue using a spinner method or the like onto a substrate that has been rubbed in one direction. By rubbing the substrate in an axially symmetrical (centrosymmetric) manner, it is possible to create polarized light with axially symmetrical (centrosymmetric) characteristics even if the methylene blue molecules are oriented in an axially symmetrical (centrosymmetric) manner. However, such a polarizing plate has poor polarization properties and has problems with durability, reproducibility, etc.

An object of the present invention is to construct a polarizing element having concentric or radial polarization characteristics, and to construct a liquid crystal element that can utilize an axially symmetrical molecular orientation characteristic.

The inventors of the present invention have taken the above-mentioned difficulties into consideration, and have devised a means for constructing a polarizing plate having axially symmetric (centrosymmetric) polarization characteristics by utilizing the orientation effect of liquid crystal molecules, and have created a liquid crystal lens with excellent molecular orientation characteristics. The present invention was completed by devising a means for achieving this.

[Means for solving the problem] In a liquid crystal cell in which liquid crystal is sealed between two glass substrates or plastic substrates, one On one substrate, the long sleeve directions of the liquid crystal molecules are aligned in one direction, and on the other substrate, they are aligned so as to be axially symmetric (centrosymmetric), that is, concentrically or radially.

Furthermore, in order to make use of the alignment effect of liquid crystal molecules caused by voltage application, a structure is adopted in which transparent conductive films are attached to two substrates. At least one of the substrates constituting the liquid crystal cell may have a curved structure or a Fresnel lens structure, and may also have a biconvex lens shape or a biconcave lens shape. It is also possible to have a configuration in which a TN liquid crystal cell is sandwiched between a linear polarizing plate and a liquid crystal cell. [Function] The alignment direction of liquid crystal molecules changes little by little with respect to the traveling direction of incident light in the liquid crystal cell. For example, in a TN liquid crystal cell in which the liquid crystal molecules are twisted 90 degrees within the liquid crystal cell, the pitch of the helical twist is four times the thickness of the liquid crystal cell, or 10 to 20 microns, which is much longer than the wavelength of light. Therefore, the polarization direction of the incident light polarized in the direction of the long axis of the liquid crystal molecules travels through the liquid crystal cell while changing along the direction of the long axes of the liquid crystal molecules (the same is true when the light is polarized perpendicular to the long axis direction). ). Therefore, when light enters through a substrate whose long axes of liquid crystal molecules are oriented in one direction, it passes through the liquid crystal layer and exits from the other substrate whose long axes are oriented in an axially symmetrical (centrosymmetric) manner. The polarized light is symmetrical (centrosymmetric). That is, by combining a homogeneous alignment in which the long axis direction of liquid crystal molecules is oriented in one direction and a substrate with an axially symmetrical (centrosymmetric) alignment, it is possible to obtain axially symmetrical (centrosymmetric) polarized light. When a liquid crystal lens is constructed in which liquid crystal molecules are oriented axially symmetrically (centrosymmetrically) on one substrate having a curved surface structure, a −-like molecular orientation state can be obtained along the wall surface on the curved surface.

[Example] As shown in Fig. 1, liquid crystal molecules are oriented in one direction (homogeneous) on the substrate 1 on the incident side, and concentrically oriented on the other substrate 2. For example, a liquid crystal 4 is sealed with an electrically insulating spacer 3 having a thickness of about 10 microns in between. FIG. 2 shows a perspective view of the liquid crystal element. Note that in FIGS. 1 and 2, the thickness of the spacer 3, that is, the thickness of the liquid crystal layer, is shown relatively larger than the thicknesses of the substrates 2 and 3. A linear polarizing plate 5 is placed on the incident side, and its polarization direction is made to match the alignment direction of liquid crystal molecules. Since the thickness of the spacer 3, that is, the thickness of the liquid crystal layer, is much larger than the wavelength of visible light, the polarization direction of the incident light changes along the alignment direction of the liquid crystal molecules. Therefore, the polarization direction of the light that has passed through the liquid crystal cell becomes the orientation direction of molecules on the output side, that is, concentric circles.

On the other hand, if the polarization direction of the linear polarizing plate 5 is oriented perpendicular to the long sleeve direction of the homogeneously aligned liquid crystal molecules on the input side substrate 1, the concentric polarization direction is rotated by 90 degrees.
A radially polarized output is obtained. As shown in FIG. 3, a TN liquid crystal cell 6 is sandwiched between a linear polarizing plate 5 and a liquid crystal cell, and a T
By applying a voltage of several volts to the N liquid crystal cell 6 using the power supply 7 and the switch 8, the polarization state shown in FIG. Since the polarization characteristics can be switched, it is possible to switch between concentric and radial polarization characteristics.

The concentric molecular orientation method can be performed by rubbing the liquid crystal cell substrate with cotton cloth, nylon cloth, etc. while rotating it, or by performing vacuum oblique vapor deposition while rotating the substrate.

Similarly, even if the liquid crystal molecules are homogeneously aligned on the light incident side substrate and radially aligned on the other substrate,
If the polarizing direction of the polarizing plate matches the orientation direction of the molecules, radial polarized light can be obtained, and if the polarizing plate is directed in a direction perpendicular to the orientation direction, concentric polarized light can be obtained. As the radial molecular orientation method, a friction method, a vacuum oblique evaporation method, etc. can be similarly used.

When a liquid crystal cell is fabricated using two substrates with transparent conductive films and a nematic liquid crystal with positive dielectric anisotropy, by applying a voltage higher than a threshold between the transparent conductive films, the liquid crystal molecules become perpendicular to the substrates. The incident light passes through the liquid crystal cell with its polarization direction unchanged. Therefore, the transmitted light becomes linearly polarized light, and it is possible to switch between axially symmetric (centrosymmetric) polarized light and linearly polarized light.

A variable focus liquid crystal lens can be constructed by forming the liquid crystal layer into a lens-like structure by forming the inner surface of at least one of the substrates having a transparent conductive film in contact with the liquid crystal with a curved surface structure or a Fresnel lens structure. Furthermore, for example, if a substrate with a curved surface structure is oriented axially symmetrically (centrosymmetrically), the liquid crystal molecules are uniformly aligned along the curved substrate, so that a high-quality liquid crystal lens can be obtained.

As a specific example, a voltage of several volts is applied using cyanopentylbiphenyl (CPB), a nematic liquid crystal with positive dielectric anisotropy, and a concave Fresnel lens with a focal length of -7.6 cm. Accordingly, it is possible to construct a variable focus lens with excellent optical characteristics, which can vary the focal length from about 15 cm to about 80 cm, has a response speed of about 1 second, and has excellent optical characteristics. Note that other liquid crystals having positive dielectric anisotropy can also be used.

Furthermore, it is possible to make the molecular orientation of the output side substrate spiral, or to have a complicated shape that is not axially symmetric (centrosymmetric).
It is also possible to easily configure polarization distribution characteristics in various forms.

[Effects of the Invention] As described above, the present invention can obtain concentric or radial axially symmetric (centrosymmetric) polarization characteristics with a simple configuration, and can apply a low voltage of about several volts to a liquid crystal cell. By applying this voltage, it is possible to switch between axially symmetric (centrosymmetric) polarized light and linearly polarized light. Furthermore, by combining it with a TN liquid crystal cell, it is also possible to switch the polarization state between concentrically polarized light and radially polarized light. Furthermore, by forming the liquid crystal layer into a lens-like or Fresnel lens-like curved surface structure, a variable focus liquid crystal lens with excellent molecular orientation characteristics can be obtained, which is an outstanding effect.

[Brief explanation of the drawing]

The drawings are for explaining the present invention in detail, and FIG. 1 is a diagram showing the configuration of a liquid crystal element that obtains concentric polarization characteristics by a liquid crystal cell constructed of substrates with homogeneous orientation and concentric orientation, and FIG. is a perspective view thereof, in which arrows indicate the polarization direction and the alignment direction of liquid crystal molecules. FIG. 3 shows a case where a TN liquid crystal cell is sandwiched between a linear polarizing plate and a liquid crystal cell. 1... Homogeneously aligned substrate 2... Concentrically aligned substrate 3... Spacer 4... Liquid crystal 5... Linear polarizing plate 6... TN liquid crystal self... Power supply 8... Switch

Claims (6)

[Claims] (1) Consists of a liquid crystal cell with liquid crystal sealed between two glass or plastic substrates and a linear polarizing plate, and on one of the substrates of the liquid crystal cell, the long axes of liquid crystal molecules are aligned in one direction. A liquid crystal element characterized in that the liquid crystal element is oriented so as to be axially symmetric (centrosymmetric), that is, concentrically or radially, on the other substrate. (2) The liquid crystal element according to claim 1, wherein a conductive film is formed on the glass substrate or plastic substrate constituting the liquid crystal cell. (3) The liquid crystal element according to claims 1 and 2, wherein at least one of the substrates constituting the liquid crystal cell has a curved inner surface in contact with the liquid crystal. (4) The liquid crystal element according to claims 1 and 2, wherein at least one of the substrates constituting the liquid crystal cell has a Fresnel lens structure. (5) The liquid crystal element according to claims 1 and 2, wherein at least one of the substrates constituting the liquid crystal cell has a biconvex lens shape or a biconcave lens shape. (6) The liquid crystal element according to claim 1, which is constructed by sandwiching a TN liquid crystal cell between a liquid crystal cell and a linear polarizing plate.