JPH05257152A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display element which can be easily produced at low cost and has excellent flexibility and to avoid cracking or peeling due to bending by constituting a transparent electrode layer of a transparent conductive film of lots of transparent conductive particles bonded with a polymer binder. CONSTITUTION:A transparent electrode layer 2 is formed by applying a coating liquid on the surface of a PET film as a transparent base material by screen printing to form a specified pattern and then irradiating the coating film with UV ray to cure. The transparent electrode layer 2 consists of lots of ITO powder particles 21, 21, bonded with a photosetting oligomer (polymer binder) 22. Then, a coating liquid prepared by dissolving a liquid crystal and PMMA in chloroform is applied on the transparent electrode layer 2 by bar coating and dried to form a polymerliquid crystal composite film 2. Another PES film 5 as a transparent base body on which a transparent electrode layer 4 is formed by the same method as for the transparent electrode layer 2 is laminated on the polymer/liquid crystal composite film 3 to manufacture the liquid crystal display element.

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 element used in a display device for TVs and general office automation equipment.

[0002]

2. Description of the Related Art In a conventional liquid crystal display device, a pair of transparent base materials having transparent electrode layers for applying a voltage to liquid crystal are fixed on the surface at intervals of several μm, and a liquid crystal material is injected into the spaces. It was formed by doing. However, with the above structure, it is difficult to manufacture a large-area display element or a flexible display element.

Therefore, recently, various liquid crystal display elements using a liquid crystal film having a self-holding shape such as a polymer / liquid crystal composite film and a polymer liquid crystal / low molecular weight liquid crystal mixed film have been proposed.
The former polymer / liquid crystal composite film is formed by casting a solution of a matrix polymer and a liquid crystal material dissolved in a solvent on one transparent substrate and drying the solution, and has a sponge structure. It has a structure in which the pores of the resulting matrix polymer are filled with liquid crystals [Polymer Preprints, Japan Vol. 3
7 , (8), 2450 (1988)].

The latter polymer liquid crystal / low molecular weight liquid crystal mixed film is a side chain type having a side chain in which a portion corresponding to a liquid crystal compound is bonded to a polymer skeleton through a flexible carbon skeleton or the like. It is formed by casting a solution of polymer liquid crystal and ordinary low-molecular liquid crystal material in a solvent on one transparent substrate, and drying and solidifying the solution. It is a mixture with a liquid crystal [JP-A-2-193
115, JP-A-2-127494, Chem.
Lett., 817 (1989), Polym. Preprints, Japan 39 (8) 23
73 (1990), etc.].

Since the composite film and the mixed film each contain a polymer, they have a self-holding shape and do not require cell gap control. Therefore, for example, by using a plastic film as a pair of transparent substrates. , Large area, and
It becomes easy to manufacture a flexible display element. The transparent electrode layer formed on the surface of the transparent substrate is conventionally prepared by a vapor phase film forming method such as a sputtering method or a vacuum deposition method.
A transparent conductive film such as a TO (indium tin oxide) film is used.

[0006]

However, since the above-mentioned conventional transparent conductive film itself has poor flexibility, when a flexible transparent substrate such as a plastic film is used, it breaks due to bending. There is a problem that peeling or peeling easily occurs. In addition, when a large-area display element is manufactured, a large-area transparent electrode layer corresponding to the large-area display element is required. Therefore, the transparent conductive film formed by the vapor phase film formation method as described above requires a large-scale manufacturing. In addition to requiring equipment, there is a problem in that a step of patterning the formed transparent conductive film by etching is required thereafter, productivity is poor, and it is difficult to reduce the manufacturing cost.

The present invention has been made in view of the above circumstances and is a liquid crystal display provided with a transparent electrode layer which is simple and inexpensive to manufacture, has excellent flexibility, and is free from cracking or peeling due to bending. The purpose is to provide a device.

[0008]

In order to solve the above problems, a liquid crystal display device of the present invention contains a liquid crystal material, and a liquid crystal film having a liquid crystal display function is provided with a transparent electrode layer on the surface thereof. In the liquid crystal display device sandwiched between a pair of transparent base materials, the transparent electrode layer is formed by a transparent conductive film in which a large number of transparent conductive particles are bonded with a polymer binder.

In the liquid crystal display device of the present invention having the above structure, since the transparent conductive film forming the transparent electrode layer has a structure in which a large number of transparent conductive particles are bound by a polymer binder, a conventional ITO film or the like is used. It has higher flexibility than In addition, the above-mentioned transparent conductive film, after applying a coating liquid in which transparent conductive particles and a thermoplastic polymer binder are dissolved or dispersed in a suitable solvent to the surface of the transparent substrate, the solvent is dried and removed. Alternatively, a transparent conductive particle and a curable polymer binder prepolymer (oligomer, monomer) are dissolved or dispersed in an appropriate solvent to apply the coating solution to the surface of the transparent substrate, and the solvent is removed by drying. In addition, since it can be formed by curing the prepolymer, a large area can be formed extremely easily without requiring a large-scale manufacturing facility such as a vapor phase film forming method.

Moreover, if various conventionally known printing methods are used for coating the surface of the transparent substrate with the coating liquid, a predetermined pattern can be formed at the same time as the coating, so that a patterning step is not required. The present invention will be described below. As the transparent conductive particles forming the transparent conductive film, the above-mentioned IT
In addition to O, particles of various conventionally known materials, such as indium-based, tin-based, and antimony-based metal complex salts, which are transparent to visible light and have conductivity, can be used.

The particle size of the transparent conductive particles is not particularly limited in the present invention, but in order to suppress light scattering and enhance the transparency of the transparent conductive film, it is not more than the wavelength of visible light, that is, 400.
The particle size is preferably nm or less. Examples of the polymer binder for binding the transparent conductive particles include acrylic polymers such as polymethylmethacrylate (PMMA) and cyclohexylmethacrylate; styrene polymers such as polystyrene; polycarbonate, aridylglycolcarbonate (CR- 39) and the like; polyester-based polymers; photo-curable polymers such as epoxy acrylates and urethane acrylates; Various polymers having excellent flexibility can be selected and used.

The thermoplastic polymer binder is soluble in the solvent used in the coating liquid and is a solvent for forming the above-mentioned polymer / liquid crystal composite film or polymer liquid crystal / low molecular liquid crystal mixed film. Insoluble ones are preferably used. In addition, the curable polymer binder usually becomes insoluble in any solvent when cured, so in the prepolymer state before curing,
It may be soluble in the solvent used for the coating liquid.

In the above transparent conductive film, it is necessary that adjacent transparent conductive particles are in contact with each other in order to impart conductivity, and for that purpose, in the transparent conductive film,
It is preferable that the content ratio of the transparent conductive particles is high. However, if the content ratio of the transparent conductive particles is too high and the content ratio of the polymer binder is relatively small, the bonding of the particles by the polymer binder becomes insufficient, resulting in the strength and flexibility of the transparent conductive film. May decrease.

In order to form a transparent conductive film having excellent conductivity and strength and flexibility without causing these problems, the content ratio of the transparent conductive particles in the transparent conductive film is 60. It is preferably in the range of 90 wt%. When the content ratio of the transparent conductive particles in the transparent conductive film is less than 60% by weight, the transparent conductive particles adjacent to each other may not contact each other as described above, and the conductivity of the film may be reduced or lost. In particular, when the content ratio of the transparent conductive particles exceeds 90% by weight, the content ratio of the polymer binder becomes relatively small, and the strength and flexibility of the transparent conductive film may be reduced.

The thickness of the transparent conductive film is not particularly limited in the present invention, but is preferably about 0.1 to 10 μm. If the thickness of the transparent conductive film is less than 0.1 μm, sufficient conductivity may not be imparted to the film, and conversely, if the thickness of the transparent conductive film exceeds 10 μm, the flexibility of the film decreases and cracking may occur. It may be easily peeled off. The transparent conductive film, as described above, the transparent conductive particles,
A coating solution prepared by dissolving or dispersing a thermoplastic polymer binder or a prepolymer of a curable polymer binder in an appropriate solvent is applied to a transparent substrate surface by various conventionally known printing methods such as a screen printing method. After coating, the solvent is dried off in the case of a thermoplastic polymer binder,
In the case of a prepolymer of a curable polymer binder, it is formed by drying and removing the solvent and curing the prepolymer.

The type of solvent may be appropriately selected depending on the type of the polymer binder described above. The transparent base material on which the transparent conductive film is formed, such as a glass plate,
Various base materials conventionally used as a transparent base material of a liquid crystal display element can be used. Among them, a liquid crystal display element having a large area and flexibility utilizing the flexibility of the transparent conductive film. A flexible plastic film that can be used as a plastic film is preferably used. As the plastic film, polyethylene terephthalate (PET) film, polyether sulfone (PES) film, etc. can be used because of its heat resistance, practical strength, optical uniformity, and the like. Is preferably used. The thickness of the plastic film is preferably about 50 to 200 μm.

As the liquid crystal film having a liquid crystal display function, the polymer / liquid crystal composite film or the polymer liquid crystal / low molecular liquid crystal mixed film is preferably used from the viewpoint of increasing the area of the device and imparting flexibility. used. As described above, the polymer / liquid crystal composite film has a structure in which the pores of a matrix polymer having a sponge structure are filled with liquid crystal, and the liquid crystal molecules in the pores are in a random state when no voltage is applied. Therefore, the incident light is scattered and is in an opaque state. When a voltage is applied to the polymer / liquid crystal composite film,
Δε> 0 [where Δε is the dielectric anisotropy, and the formula:

[0018]

[Equation 1]

Is represented by (note that

[0020]

[Outer 1]

Is the dielectric constant in the molecular axis direction,

[0022]

[Outside 2]

Is the dielectric constant in the direction orthogonal to the molecular axis)], the liquid crystal molecules are oriented in the direction of the electric field by the electro-optical effect, and the incident light can pass through without being scattered, resulting in a transparent state. Switch to a state. A normal nematic liquid crystal is suitable as the liquid crystal used in the polymer / liquid crystal composite film. As a liquid crystal material, the dielectric anisotropy Δε
Is preferable in order to obtain good characteristics.

As the matrix polymer, those having high transparency to visible light are preferable, and for example, (meth) acrylic polymer represented by PMMA is preferably used.
In order to impart flexibility, it is preferable to select and use one having higher flexibility among the above acrylic polymers. In addition, the matrix polymer has improved adhesion to the transparent electrode layer of the composite film to prevent positional displacement and peeling between the two, and makes it easier to increase the area of the liquid crystal display device and impart flexibility. Therefore, an adhesive polymer or an adhesive polymer can be used together.

As the adhesive polymer and the adhesive polymer, it is preferable to use those having excellent compatibility with the matrix polymer in order to maintain the transparency of the matrix polymer. PMMA as a molecule
In the case of using, a (meth) acrylic adhesive polymer or adhesive polymer is preferably used. When a low-frequency or direct-current electric field is applied, the latter polymer liquid crystal / low-molecular liquid crystal mixed film causes turbulence due to the movement of electric charges associated with the frequency in the film, so that the incident light is strongly scattered. And becomes opaque. On the other hand, when a high frequency electric field is applied,
The liquid crystal molecules in the film are homeotropically oriented in the direction of the electric field so that the incident light can pass through without being scattered, and it is converted to a transparent state. In addition, this polymer liquid crystal / low molecular weight liquid crystal mixed film has a memory property of stably holding a light scattering state or a non-scattering state when the electric field is removed in both of the above states.

The film thickness of the polymer / liquid crystal mixed film and the polymer liquid crystal / low molecular liquid crystal composite film needs to be equal to or more than the wavelength of visible light in order to form a light scattering type liquid crystal display device. However, if the film thickness is too large, the driving voltage of the device becomes too high, so in practice, about 5 to 30 μm is appropriate.
In order to make the liquid crystal display device a color display type, various kinds of conventionally known dyes can be added to the mixed film and the composite film.

In some cases, in order to prevent the liquid crystal from swelling in the transparent conductive film, or conversely, components in the transparent conductive film from diffusing into the liquid crystal layer and adversely affecting the liquid crystal layer, the liquid crystal layer and the transparent conductive film may be adversely affected. A barrier layer may be provided. It is desirable that the thickness of the barrier layer be as thin as possible from the two viewpoints of (1) ensuring transparency and (2) suppressing the reduction of the electric field applied to the liquid crystal. The film thickness depends on the material, but 0.01 to 2μ
It is preferable to select in the range of m. Although various polymer materials are used as the material, the same material as the above-mentioned polymer binder can be used from the viewpoint of transparency.

[0028]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Example ITO powder as transparent conductive particles (average particle size 50 nm)
90 parts by weight and a urethane acrylate-based photocurable oligomer as a prepolymer of a curable polymer binder (trade name “Aronix M905 manufactured by Toagosei Kagaku KK”
0) 10 parts by weight and 1 part by weight of a polymerization initiator (trade name “Darocur 1173” manufactured by Merck & Co., Inc.) were added to acetone 30 parts.
A coating liquid was prepared by uniformly stirring and mixing with 0 part by weight.

This coating solution was applied to a transparent substrate having a thickness of 10
As shown in FIG. 1, the surface of a 0 μm PET film was printed in a predetermined pattern shape by a screen printing method and then irradiated with ultraviolet rays to be cured.
A large number of ITO powders 21, 21 are formed on the surface of the ET film 1.
Form a transparent electrode layer 2 having a thickness of about 1.5 μm, which is bonded with the cured product 22 of the photocurable oligomer.

Next, 6 parts by weight of a liquid crystal (trade name E63 manufactured by Merck Japan) and 4 parts by weight of PMMA were dissolved in chloroform to prepare a coating solution having a concentration of 15% by weight on the transparent electrode layer 2. Was coated by a bar coating method and dried to form a polymer / liquid crystal composite film 3 having a thickness of about 20 μm. Then, in the same manner as described above, a thickness of about 1.
P as a transparent substrate on which a transparent electrode layer 4 of 5 μm is formed
The ES film 5 was laminated on the polymer / liquid crystal composite film 3 to produce a liquid crystal display element. In addition, this PE
The S film 5 was overlapped with the PET film 1 with a shift of about 3 mm as shown in the figure in order to connect wirings for voltage application to both transparent electrode layers 2 and 4.

The obtained liquid crystal display element was in a white turbid state with a linear light transmittance of 5% when no voltage was applied, and when an AC voltage of 200 Hz and 50 V was applied between the transparent electrode layers 2 and 4, linear light was emitted in 2 ms. It was converted to a light transmission state with a transmittance of 75%. Moreover, when the voltage application was stopped, the white turbid state was restored in 10 ms. The liquid crystal display device was repeatedly bent 20 times with a radius of curvature of 5 mm, and the state was observed. As a result, no cracks or peeling were observed in both transparent electrode layers 2 and 4. When an AC voltage was applied in the same manner as above and the linear light transmittance and its conversion time were measured, the same results as before bending were obtained.

Comparative Example A liquid crystal display device was produced in the same manner as in the above-mentioned example except that an ITO thin film as a transparent electrode layer was formed on the surfaces of the PET film 1 and the PES film 5 by the sputtering method. For this liquid crystal display element, an AC voltage was applied in the same manner as above, and the linear light transmittance and its conversion time were measured. As a result, the same results as in the example were obtained before bending. However, after repeatedly bending 20 times with a radius of curvature of 5 mm, the state was observed, and it was observed that a large number of cracks and peeling had occurred in the ITO thin film, and it did not operate even when an AC voltage was applied.

[0033]

As described above, the liquid crystal display device of the present invention has a structure in which the transparent conductive film forming the transparent electrode layer has a structure in which a large number of transparent conductive particles are bonded with a polymer binder. It has higher flexibility than the ITO film and the like. Further, since the transparent conductive film is formed by applying a coating solution containing the above-mentioned components, it does not require a large-scale manufacturing facility such as a vapor phase film forming method. By using various known printing methods, a predetermined pattern can be formed at the same time as the application, so that it is possible to easily and inexpensively manufacture, such as not requiring a patterning step.

Therefore, the liquid crystal display device of the present invention having the above-mentioned transparent electrode layer can be suitably used as a display device having a large area and flexibility.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a layer structure of a liquid crystal display element of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Transparent base material (PET film) 2 Transparent electrode layer 3 Liquid crystal film (polymer / liquid crystal composite film) 4 Transparent electrode layer 5 Transparent base material (PES film) 21 Transparent conductive particles (ITO powder) 22 Polymer binder (light) Cured product of curable oligomer)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Koji Hara, 1-3-1 Shimaya, Konohana-ku, Osaka No. 3 Sumitomo Electric Industries, Ltd. Osaka Works

Claims (1)

[Claims] 1. A liquid crystal display device comprising a liquid crystal film containing a liquid crystal material and having a liquid crystal display function sandwiched between a pair of transparent base materials having a transparent electrode layer on the surface thereof, wherein the transparent electrode layer comprises:
A liquid crystal display device comprising a transparent conductive film in which a large number of transparent conductive particles are bonded with a polymer binder.