JPH0792451A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display element which is simple in structure, is easily formable to a large size, has a steep threshold characteristic in an electro-optic characteristic and is suitable for simple matrix driving. CONSTITUTION:This liquid crystal display element has a pair of substrates which are formed with electrodes on the main surfaces of one side and a liquid crystal material which is clamped between a pair of these substrates arranged in such a manner that these electrodes face each other. The liquid crystal material is dispersed in a high polymer matrix. The liquid crystal molecules 21 of the liquid crystal material rise to align in the direction of an electric field when the electric field is impressed between the electrodes. The liquid crystal molecules have a spiral structure and are arranged in such a manner that their spiral axes align when the electric field is not impressed between the electrodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art In general, a liquid crystal display element is composed of two substrates which are arranged to face each other with a predetermined gap, and a liquid crystal material which is sealed between the substrates. In this liquid crystal display element, for example, wiring and transparent electrodes are formed on a glass substrate, and an electrically insulating alignment film imparting liquid crystal alignment is formed on the wiring and transparent electrodes. The glass substrates are arranged with the electrode surfaces facing each other, and
In order to maintain the space between the glass substrates, a minute spacer material made of glass fiber, resin beads, or the like is interposed, and a liquid crystal material is injected between the glass substrates.

Among liquid crystal display devices, a super-matrix nematic (hereinafter abbreviated as STN) liquid crystal display device of a simple matrix display system has been put into practical use as a device used in personal computers and the like.

In this STN liquid crystal display device, two alignment films are respectively subjected to alignment treatment, and two glass substrates are arranged so as to be twisted so that the longitudinal directions thereof form a predetermined angle. In this case, since the liquid crystal molecules are arranged along the direction of the alignment treatment, the liquid crystal material sandwiched between the two glass substrates has a twisted structure.

When an electric field above the threshold is applied to this STN liquid crystal display element, the liquid crystal molecules arranged in the twisted structure are arranged in the electric field direction. Also, when the application of the electric field is stopped,
The liquid crystal molecules return to their original twist structure. In this way, the polarization state of the transmitted light is switched by applying an electric field above the threshold value and stopping the application of the electric field. Therefore, this ST
The N liquid crystal display element is suitable for a display driven by a simple matrix.

On the other hand, there is a polymer dispersed liquid crystal as a liquid crystal display device which does not require an alignment film and can be easily enlarged. This polymer-dispersed liquid crystal is obtained by encapsulating a liquid crystal with polyvinyl alcohol or the like to prepare liquid crystal droplets and dispersing the liquid crystal droplets in a polymer (Japanese Patent Laid-Open No. 58-501632).
Gazette, U.S. Pat. No. 4,435,047).

In this polymer-dispersed liquid crystal, if the encapsulated liquid crystal molecules have a positive dielectric anisotropy, they are aligned in the direction of the electric field in the presence of an electric field to have a refractive index n _o . It develops transparency when n _o is equal to the refractive index n _{p of the} polymer. Also, when removing the electric field, the liquid crystal molecules to return to a random sequence, the refractive index is clouded by scatter light at the interface between the liquid crystal droplets and the polymer deviates from n _o. In this way, the transmitted light is switched. Other examples of polymer-dispersed liquid crystals are those in which liquid crystals are dispersed in epoxy resin (JP-A-61-250218) and those in which liquid crystals are dispersed in urethane acrylate resin (JP-A-2- No. 83534).

[0008]

Since the STN liquid crystal display element utilizes the birefringence effect of a liquid crystal material having a twisted structure, it is necessary to control the substrate spacing with high accuracy, and a large liquid crystal display element is required. It cannot be made.

Further, the polymer dispersion type liquid crystal display element has a simple structure, is easy to manufacture and can be made large in size, but since it does not have a steep threshold characteristic in electro-optical characteristics, it is a simple matrix. Not suitable for driving.

The present invention has been made in view of the above points, has a simple structure, can be easily enlarged, and has a steep threshold value in electro-optical characteristics, and is suitable for simple matrix driving. The purpose is to provide.

[0011]

According to the present invention, a liquid crystal material sandwiched between a pair of substrates having electrodes formed on one main surface and a pair of substrates arranged so that the electrodes face each other. In the liquid crystal display element, the liquid crystal material rises so that liquid crystal molecules of the liquid crystal material are perpendicular to the substrate when a voltage is applied between the electrodes in a polymer matrix. The liquid crystal display device is characterized in that the liquid crystal molecules are arranged in a spiral structure so that a spiral axis is perpendicular to the substrate when no voltage is applied therebetween.

Here, as the substrate, a glass substrate, a film substrate or the like can be used. In addition, ITO or the like can be used as the electrode material.

An ultraviolet curable resin such as an acrylate resin can be used as the polymer matrix constituting the liquid crystal material. The ultraviolet curable resin can be prepared, for example, by mixing a monomer, an oligomer, a photopolymerization initiator and the like.

When a voltage is applied between the electrodes in the polymer matrix, the liquid crystal molecules rise so as to be perpendicular to the substrate, and when no voltage is applied between the electrodes, the liquid crystal molecules have a helical structure and have a spiral axis. As a liquid crystal material that is arranged so as to be perpendicular to the substrate, for example, a dual frequency drive type liquid crystal can be mentioned. The dual frequency drive type liquid crystal is a nematic liquid crystal that changes the sign of the dielectric anisotropy from positive to negative when the frequency of the applied voltage is increased, and examples thereof include organic compounds shown in Chemical formulas 1 and 2.

[0015]

[Chemical 1]

[Chemical 2] As a method of arranging the liquid crystal molecules in a spiral structure having a spiral pitch p, a method of adding a chiral agent to a liquid crystal material or the like can be used. In this case, the addition amount of the chiral agent is preferably determined appropriately so as to satisfy p / 2 <d <p in consideration of the kind of the chiral agent.

The spiral pitch p and the area size d are p / 2 <
It is set so as to satisfy the relationship of d <p. This is because if the area size d is half the spiral pitch p / 2 or less, the electro-optical characteristics do not have steepness, and if the area size d is the spiral pitch p or more, coloring due to selective reflection occurs. The area size d of the two-frequency drive type liquid crystal means an area occupied by the two-frequency drive type liquid crystal in a direction substantially perpendicular to the substrate surface, and the spiral pitch p means that the spiral axis is the substrate surface. It means the pitch when the direction is almost perpendicular to.

The shape, size and the like of the dual frequency drive type liquid crystal region are determined by the compatibility between the polymer matrix and the dual frequency drive type liquid crystal, the conditions for preparing the polymer matrix and the like.
For example, when an ultraviolet curable resin is used as the polymer matrix, the size of the region is reduced by increasing the intensity of ultraviolet light and curing it. Therefore, in the actual manufacturing, p / 2 <d should be taken into consideration in consideration of the compatibility between the polymer matrix and the two-frequency drive type liquid crystal and the conditions for preparing the polymer matrix.
The addition amount of the chiral agent is determined so that <p is satisfied.

[0018]

In the liquid crystal display element of the present invention, the liquid crystal material rises so that the liquid crystal molecules are perpendicular to the substrate when a voltage is applied between the electrodes, and the liquid crystal molecules are formed when no voltage is applied between the electrodes. It is characterized in that the spiral structure is arranged so that the spiral axis is perpendicular to the substrate.

The operation in this case will be described using a dual frequency drive type liquid crystal.

The area size d and the spiral pitch p are p / 2 <
When the relationship of d <p is satisfied, the twist angle of the spiral structure is 36.
It is less than 0 °. Therefore, in a state where no electric field is applied, that is, in a scattering state, a phenomenon such as selective scattering of cholesteric liquid crystal does not occur. In this state, the liquid crystal molecules in the polymer matrix are not perpendicular to the substrate surface 11, that is, not parallel to the traveling direction of the incident light, as shown in FIG. Most of the incident light is not index-matched and is scattered.

On the other hand, when an electric field is applied, that is, in a transmissive state, the liquid crystal molecules in the polymer matrix are shown in FIG.
As shown in (B), the direction perpendicular to the substrate surface 11,
That is, since the light is arranged in the traveling direction of the incident light, the incident light is transmitted as it is. The liquid crystal molecules of this dual frequency drive type liquid crystal are
When an electric field is applied, it immediately aligns in the direction of the electric field, and therefore exhibits steep rising characteristics in electro-optical characteristics. Therefore, the switching of transmission / scattering of incident light by applying the electric field and stopping the application of the electric field is suitable for simple matrix driving.

Further, since the liquid crystal display device of the present invention has a structure in which the two-frequency drive type liquid crystal is dispersed in the polymer matrix, an alignment film and an external optical element are not required, and therefore it can be obtained easily and at low cost. be able to.

[0023]

【Example】

Example 1 11% by weight of butyl acrylate, acrylic oligomer M-
A prepolymer was prepared by mixing 8% by weight of 1200 (manufactured by Toagosei Co., Ltd.) and 1.0% by weight of Darocur 1116 (manufactured by Merck Ltd.) as a photo-curing initiator. In addition, a dual-frequency drive type liquid crystal in which two types of liquid crystal shown in Chemical formulas 1 and 2 are mixed in equal amounts is used as a chiral agent with C15.
A liquid crystal mixture was prepared by adding 100% by weight (manufactured by Merck & Co., Inc.). At this time, in the initial two-frequency drive type liquid crystal, as shown in FIG. 2, the liquid crystal molecules 21 are arranged without taking a helical structure, and by adding a chiral agent, as shown in FIG. The liquid crystal molecules 21 come to have a spiral structure.

Then, 80% by weight of the liquid crystal mixture was added to the prepolymer and mixed to prepare a mixed solution.

Next, ITO electrodes were formed as transparent electrodes on each of the two glass substrates, and the distance between the substrates was 13 μm.
A liquid crystal cell was prepared by arranging them so as to face each other. Then, a prepolymer in which the liquid crystal mixture was dispersed was injected between the glass substrates of this liquid crystal cell.

Next, a voltage higher than a threshold value of a frequency higher than the crossover frequency (a frequency at which Δε <0), for example, an alternating voltage of 20 kHz at 10 kHz is applied to the liquid crystal cell, and an ultraviolet irradiation device mini-cure 450 (Ushio). The prepolymer was exposed for 2 minutes using a product of Denki Co., Ltd.). At this time, the liquid crystal molecules in the prepolymer are arranged so that the spiral axis of the spiral structure is substantially perpendicular to the substrate surface, as shown in FIG. Thus, the liquid crystal display element of the present invention was produced.

The electro-optical characteristics of the obtained liquid crystal display device were examined. The result is shown in FIG. The electro-optical characteristics were measured by the device shown in FIG. This device comprises a helium-neon laser 31, a lens 32, an aperture 33, and a photodiode 34 arranged in parallel. The measurement of the electro-optical characteristics is performed by using the liquid crystal display element 35 between the helium-neon laser 31 and the lens 32.
With a wavelength of 633 nm and an output of 0.5 mW, with a function generator for the liquid crystal display device, 1 kH
z, square voltage was applied. Further, in order to clarify the effect of the liquid crystal display element of the present invention, the electro-optical characteristics of the ordinary polymer dispersion type liquid crystal display element were examined in the same manner as above. The results are also shown in FIG.

As is apparent from FIG. 5, the liquid crystal display element of the present invention was found to have steepness in electro-optical characteristics.
On the other hand, in the ordinary polymer dispersion type liquid crystal display element, steepness in electro-optical characteristics was not recognized.

Further, since the liquid crystal display device of the present invention does not require an alignment film, it is possible to omit the steps such as alignment treatment, and it is not necessary to provide an optical element such as a polarizer arranged outside, so that it can be easily manufactured. did it.

Example 2 15% by weight of isododecyl acrylate, long-chain aliphatic diacrylate C-2000 (trade name, manufactured by SATOMER) 10
% By weight, and Darocur 111 as photocuring initiator
6 (manufactured by Merck & Co., Inc.) 1.0 wt% was mixed to prepare a prepolymer.

Then, 74% by weight of the liquid crystal mixture prepared in Example 1 was added to the prepolymer and mixed to prepare a mixed solution.

Next, ITO electrodes were respectively formed as transparent electrodes on the two glass substrates, and the distance between the substrates was 10 μm.
A liquid crystal cell was prepared by arranging them so as to face each other. Then, a prepolymer in which the liquid crystal mixture was dispersed was injected between the glass substrates of this liquid crystal cell.

Next, the liquid crystal cell was filled with 10 kHz, 20
By applying an AC voltage of V, the UV irradiator MiniCure 4
50 was used to expose the prepolymer for 1 minute to prepare a liquid crystal display device of the present invention.

About the obtained liquid crystal display device, Example 1
When the electro-optical characteristics were examined in the same manner as in, the steepness in the electro-optical characteristics was confirmed as shown in FIG.

Since the liquid crystal display element of the present invention performs switching in the scattering-transmission mode, it has a high light utilization efficiency and is suitable for a reflection type, particularly a projection type display element. Therefore,
The liquid crystal display device of the present invention is expected to be applied to a substitute medium for an OHP sheet, a rewritable electronic notebook, a large bulletin board, a personal computer and the like.

[0036]

As described above, in the liquid crystal display element of the present invention, when the liquid crystal material is applied with a voltage between the electrodes, the liquid crystal molecules rise so as to be perpendicular to the substrate, and the voltage is applied between the electrodes. When the liquid crystal molecules are not aligned, the liquid crystal molecules are arranged in a spiral structure so that the spiral axis is perpendicular to the substrate. Therefore, it is easy to increase the size with a simple structure. It is suitable for matrix driving.

[Brief description of drawings]

FIG. 1A is a schematic view showing an arrangement state of liquid crystal molecules in a non-electric field application state, and FIG. 1B is a schematic view showing an arrangement state of liquid crystal molecules in an electric field application state.

FIG. 2 is a schematic view showing liquid crystal molecules of a dual frequency drive type liquid crystal before adding a chiral agent.

FIG. 3 is a schematic view showing liquid crystal molecules of a dual frequency drive type liquid crystal after adding a chiral agent.

FIG. 4 is a schematic diagram showing liquid crystal molecules in a prepolymer after exposure while applying a voltage.

FIG. 5 is a graph showing electro-optical characteristics of the liquid crystal display device of the present invention.

FIG. 6 is a diagram for explaining an apparatus for measuring electro-optical characteristics of the liquid crystal display element of the present invention.

[Explanation of symbols]

11 ... Substrate surface, 21 ... Liquid crystal molecule, 31 ... Helium-neon laser, 32 ... Lens, 33 ... Aperture, 34 ... Photodiode, 35 ... Liquid crystal display element.

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[Procedure amendment]

[Submission date] October 14, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011]

According to the present invention, a liquid crystal material sandwiched between a pair of substrates having electrodes formed on one main surface and a pair of substrates arranged so that the electrodes face each other. in the liquid crystal display device having a preparative, liquid crystal material is dispersed in a polymer matrix, between the electrodes
When an electric field is applied, the liquid crystal molecules of the liquid crystal material are
A liquid crystal display device is provided, which rises so as to be aligned in the direction of an electric field, and is arranged such that the liquid crystal molecules have a helical structure and the helical axes are aligned when an electric field is not applied between the electrodes.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

Dispersed in a polymer matrix, liquid crystal molecules are oriented in the direction of the electric field when an electric field is applied between the electrodes.
An example of a liquid crystal material in which liquid crystal molecules have a spiral structure and are aligned so that their helical axes are aligned when no electric field is applied between the electrodes is a dual frequency drive type liquid crystal. The dual frequency drive type liquid crystal is a nematic liquid crystal that changes the sign of the dielectric anisotropy from positive to negative when the frequency of the applied voltage is increased, and examples thereof include organic compounds shown in Chemical formulas 1 and 2.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

[0018]

In the liquid crystal display element of the present invention, liquid crystal molecules are aligned in the direction of the electric field when an electric field is applied between the electrodes as the liquid crystal material.
Cormorant As rise, even the liquid crystal molecules are arranged so that the helical axes are aligned in a helical structure when no electric field is applied between the electrodes
It is characterized by the use of the.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

[0036]

As described above, in the liquid crystal display device of the present invention, when the liquid crystal material rises so that the liquid crystal molecules are aligned in the direction of the electric field when an electric field is applied between the electrodes and no voltage is applied between the electrodes. The liquid crystal molecules have a spiral structure and the spiral axes are aligned.
Since sequence as earthenware pots, is easily large-sized with a simple structure, it is suitable for simple matrix driving has a steep threshold characteristics in the electro-optical properties.

Claims (1)

[Claims] 1. A liquid crystal display device comprising: a pair of substrates having electrodes formed on one main surface; and a liquid crystal material sandwiched between the pair of substrates arranged so that the electrodes face each other. When the voltage is applied between the electrodes in the polymer matrix, the liquid crystal material rises so that the liquid crystal molecules of the liquid crystal material are perpendicular to the substrate, and when no voltage is applied between the electrodes. The liquid crystal display device is characterized in that the liquid crystal molecules are arranged in a spiral structure so that a spiral axis is perpendicular to the substrate.