JP3137275B2 - Liquid crystal display device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermo-optical and electro-optical display device using transmitted light and scattered light, and more particularly to a transmission / scattering mode liquid crystal display device having a three-dimensional network structure and a liquid crystal, and a method of manufacturing the same. .

[0002]

2. Description of the Related Art Hitherto, liquid crystals have been generally used as thermo-optical and electro-optical display devices. For example, display devices using a twisted nematic (TN) liquid crystal or a ferroelectric liquid crystal are known.

[0003] In these display elements, the process is complicated to obtain a large-area display element, and the liquid crystal held between the substrates cannot maintain uniformity due to its own weight, resulting in poor display quality. It had many technical problems. Furthermore, these display elements, whether of the direct-view type or the projection type, require a polarizing plate in terms of display principle, and thus have a problem of low light utilization.

In contrast to the above display elements, a phase change type liquid crystal display element using cholesteric liquid crystal and a display element using the dynamic scattering effect of nematic liquid crystal do not require a polarizing plate and thus have a high light utilization rate. These display elements are excellent in that they have a wide viewing angle. However, these display elements require a high driving voltage and have the same technical problems as the above-described display elements in increasing the area.

To solve the above problem, a display device having a nematic liquid crystal capsule (Japanese Patent Publication No. 58-501631)
Also, a display element in which liquid crystal droplets are dispersed and held in an epoxy resin (Japanese Patent Publication No. 61-502128) has been proposed. These are called polymer dispersion type liquid crystal display devices in transmission / scattering mode, and do not require a polarizing plate, so that the light utilization is high,
Although it is advantageous in manufacturing a display element having a larger area,
There is a problem that the driving voltage is high.

Further, a transmission / scattering mode polymer-dispersed liquid crystal display device using a photocurable compound as a matrix (JP-A-63-271233, JP-A-1-198)
726) has been proposed, and according to this, the drive voltage is reduced.

[0007] These polymer-dispersed liquid crystal display elements are liquid crystal display elements in which liquid crystal is dispersed and held in a three-dimensional network structure, have a high light utilization factor, and can be sufficiently combined with a schlieren optical system. It has the advantage that a contrast ratio can be obtained and the system configuration is simple, and research and development are currently being actively conducted.

However, the above-mentioned liquid crystal display element has problems in that the display quality, that is, the image quality as a display, is lower than that of a conventional liquid crystal display element in terms of hysteresis and inferior temperature characteristics. Due to the problem, there is also a problem that it is technically difficult to manufacture a uniform element.

In a similar attempt, US Pat.
There is also known a polymer-impregnated liquid crystal display device in which an optical modulation material such as a liquid crystal is impregnated using a porous polymer as a matrix proposed in the specification of Japanese Patent No. 411495. This display element also has advantages such as a high light utilization factor and a wide viewing angle similarly to the above-mentioned polymer dispersion type liquid crystal display element, but it has hysteresis, is inferior in temperature characteristics, and has a uniform element. It still has the problem of being relatively difficult to manufacture.

In view of the above problems of the prior art, the present inventors have developed a polymer-impregnated liquid crystal display of transmission / scattering mode using a porous film having a controlled surface energy, which has been made porous by stretching, as a matrix. Provide the element
Was. According to this, there is an advantage that a good display can be obtained by improving the hysteresis and temperature characteristics, and a relatively uniform porous film can be obtained, so that a uniform element can be manufactured.

[0011]

The problem to be solved by the present invention is to solve the problems of the prior art . In the above-mentioned polymer-impregnated liquid crystal display device in the transmission / scattering mode, the above-mentioned porous material is used. When the film is formed by stretching, it is difficult to control the network diameter of the three-dimensional network structure. In particular, when trying to obtain a porous film having a porosity of 80% or more, the network diameter is 0.05 μm or less. Very thin fibers are likely to be produced. In addition, a beard-like fiber in which the three-dimensional structure is partially broken and is not connected between meshes is likely to be generated. Such a liquid crystal display element using a three-dimensional network structure having a very thin fiber or a fiber having one end at a free end as a matrix has a thickness of 0.05 μm or less due to the movement of the liquid crystal molecules due to the electric field response. In order to move a fiber having a diameter or a portion which is not connected between meshes and is not subjected to tension in a whisker-like three-dimensional mesh structure, the voltage of the liquid crystal display element is reduced.
Hysteresis is relatively likely to appear in the transmittance characteristics. Therefore, there is a problem that gradation display is difficult, and further improvement has been desired.

In the transmission / scattering mode polymer-dispersed liquid crystal element as well, if the content of the liquid crystal is increased, it is difficult to control the network diameter of the three-dimensional network polymer compound, and the matrix becomes an island. Hysteresis appears in the same manner as in the polymer-impregnated liquid crystal display device described above because the film has a portion that is easily scattered or has a free end at one end in a film shape.

Here, the hysteresis described in the present invention will be described. The hysteresis is as shown in FIG.

[0014]

(Equation 1)

T = Transmittance value with a change rate of 50% at the time of rising ΔT = A value represented by an increase of the transmittance at the time of falling at the same voltage as the change rate of 50% at the time of rising.

The porosity described in the present invention is:

[0017]

(Equation 2)

X = weight when impregnated with a liquid having a known specific gravity Y = weight when only three-dimensional network structure is used.

The present invention has been made in order to improve these disadvantages of the prior art. Even when a three-dimensional network structure having a high porosity is used for a matrix, the strength of the matrix is sufficient, and It is an object of the present invention to provide a liquid crystal display element with good contrast, in which an unstable matrix which is easy to move is substantially eliminated and hysteresis is reduced.

[0020]

Means for solving the problem of the present invention, in order to solve the problem] is achieved by a liquid crystal display device and a manufacturing method thereof according to the invention described below. That is, the present invention relates to a liquid crystal display element having a three-dimensional network structure and a liquid crystal between a pair of substrates which may have a transparent electrode on at least one side, wherein the three-dimensional network structure is stretched. By porosity
Porous film having a porosity of 80 to 98%.
And the thickness of the three-dimensional network structure is 0.2
A liquid crystal display device comprising a polymer film having a thickness of about 2 μm .

The present invention also relates to a method for manufacturing a liquid crystal display device having a three-dimensional network structure and a liquid crystal between a pair of substrates, at least one of which may have a transparent electrode. A method for manufacturing a liquid crystal display element, comprising: forming a polymer film having a thickness of 0.2 to 2 μm on a three-dimensional network structure; and impregnating and injecting a liquid crystal.

Further, the present invention is the above-mentioned liquid crystal display device, wherein the three-dimensional network structure polymer compound is a porous film made porous by stretching, and the porous film has a porosity of 80% or less. 98% and 0.05μ
m or less.

Hereinafter, the present invention will be described in more detail. Book
In the present invention, the three-dimensional network structure has a property of randomizing the liquid crystal and scattering light. The higher the porosity, the higher the content of the liquid crystal, which is preferable for improving the light transmittance, lowering the threshold voltage, and improving the contrast. However, those having a high porosity, that is, those having a high liquid crystal content, have a problem in that the strength tends to be insufficient and the characteristics tend to be unstable.

The present inventors have conducted intensive studies and found that 3
By coating a two-dimensional network structure with a polymer film having a thickness of 0.2 to 2 μm, the strength of the fine fiber portion of the network structure is improved, and the unconnected unstable parts in the network structure are improved. The three-dimensional network structure having a high porosity and substantially eliminating the portion was obtained.

When the thickness of the polymer film is less than 0.2 μm, the strength of the unstable portion cannot be sufficiently obtained, and the effect cannot be expected. When the thickness is more than 2 μm, the content of the liquid crystal increases. And the light transmittance is reduced, thus deteriorating the contrast.

Since the polymer film used in the present invention needs to have sufficient strength, a polymer compound having a high molecular weight is selected. That is, the average degree of polymerization is 400 to 2
0000 high molecular compounds are preferably used. This is because a polymer compound having an average degree of polymerization of less than 400 is inferior in material strength, and a polymer compound having an average degree of polymerization exceeding 20,000 is difficult to process. This polymer film can be easily obtained by dissolving a polymer compound having the above average degree of polymerization into a solution and impregnating the polymer into a three-dimensional network structure, followed by drying. However, the polymer film is impregnated and dried using a polymerizable composition. Thereafter, or simultaneously, the polymer may be cured to form a film of the polymer having the above average degree of polymerization. Moreover, you may mix and process a plasticizer as needed at the time of a process.

Further, as the polymer film used in the present invention,
A suitably selected polymer compound has a tensile modulus of 0.2
× 10 ⁴ Kg / cm ^{2 to} 20 × 10 ⁴ Kg / cm ² , more preferably 0.3 × 10 ⁴ Kg / cm ² to 15
× 10 ⁴ Kg / cm ² is desirable.

The tensile modulus is determined by a tensile test (for example, JIS K6723, K
6745, K6911, and ASTM D638) can be easily obtained from the following equation from the stress-strain curve obtained.

[0029]

(Equation 3)

P = Load at elongation Δ1 (Kg) L = Distance between mark lines (cm) A = Cross-sectional area of sample piece (cm ² ) Δ1 = Elongation between mark lines (cm)

Thus, the present inventors have found that in order to satisfy various characteristics by impregnating the liquid crystal into the three-dimensional network structure provided with the polymer film, it is necessary to use a polymer compound, a liquid crystal and the like to be used. Although it is necessary to select a liquid crystal display device, a liquid crystal display device having high light transmittance, good contrast, and reduced hysteresis was obtained.

Further, a high quality liquid crystal display device can be obtained by using the liquid crystal display element of the present invention. Further, the present invention can be suitably used for a direct-view display device.

Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a sectional view showing an example of the liquid crystal display device of the present invention. In FIG.
For 1 ', glass, plastics or the like can be used. The electrodes 102 and 102 ′ are made of a transparent electrode such as ITO (indium tin oxide) or SnO ₂ ,
1, a metal film of Ag, Cu, Cr or the like is used.

Further, the adhesive layers 103, 103 'are formed on the electrodes.
Is provided as needed. The adhesive layer is a porous film,
The selection is made according to a substance that comes into contact with an adhesive such as an electrode and an adhesive such as a liquid crystal. For example, adhesives of cyanoacrylate type, polyester acrylate type, chloroprene type, nitrile rubber type, epoxy type, polyurethane type and the like can be used. Further, if necessary, an insulating layer (not shown) and / or
Alternatively, an alignment film may be provided, or an adhesive layer or an insulating layer may be provided with an alignment regulating force for the liquid crystal.

As the three-dimensional network structure 104,
Hypore 1000, 2000, 3000 (manufactured by Asahi Kasei Corporation), KT-50, LE-85, Duracard,
A porous film such as Exepol (manufactured by Mitsubishi Kasei Kogyo Co., Ltd.) or Fluoropore (manufactured by Sumitomo Electric Industries, Ltd.) can be suitably used. Further, a homogeneous solution of a photopolymerizable compound and a low-molecular compound may be subjected to photopolymerization and phase separation, and then the low-molecular compound may be extracted to form a three-dimensional network structure. Alternatively, a dispersion obtained by applying and drying a dispersion solution of a low molecular compound and an incompatible high molecular compound and extracting the low molecular compound may be used.

Specifically, as a material which is phase-separated into a three-dimensional network structure, a monomer having a vinyl group such as styrene, chlorostyrene or dizinylbenzene, a monomer or oligomer such as an acrylate or methacrylate is typically used. And a polymerization initiator such as a carbonyl compound, a sulfur compound and a halogenated compound. Further, if necessary, additives such as a polymerization initiation auxiliary agent may be added thereto. As a low molecular weight compound, for example, nematic liquid crystal, EDH-37, E-44 manufactured by BDH, ZLI-2008 manufactured by Merck, manufactured by Roche A mixture of RO-TN-403 and the like can be used. When a low-molecular compound is extracted from a dispersion solution to form a three-dimensional network structure, a low-molecular-weight solid and / or incompatible with high-molecular compounds such as polyurethane, polyamide, polyimide, polystyrene, polycarbonate, and polymethacrylate. Alternatively, it can be used by mixing with a liquid.

The polymer film 10 used in the present invention is
As 5, a polymer compound incompatible with the liquid crystal to be impregnated is selected. Also, from the strength required when forming the polymer film, a polymer compound having an average degree of polymerization of 400 to 20,000,
Also, the tensile modulus of elasticity is 0.2 × 10 ⁴ Kg / cm ² -20 × 1
0 ⁴ ones Kg / cm ^2, more preferably, 0.3 × 1
0 of ^{4 Kg / cm 2 ~15 × 10} 4 Kg / cm 2 that is preferably chosen. For the purpose of enhancing thermal stability, a polymer film having a glass transition temperature of usually 50 ° C. or higher, preferably 80 ° C. or higher is selected. Furthermore, the softening temperature is 60
C. or higher, preferably 90 C. or higher.

Specifically, from various thermoplastic resins, thermosetting resins, etc., polyurethane, polyamide, polyimide,
Examples include polystyrene, polyacrylate, polymethacrylate, polysulfone, cellulose, polyvinylidene fluoride, polyvinyl chloride, polyamideimide, polyfluorocarbon, silicone resin, and phenol resin. Further, an additive such as a plasticizer may be added as necessary.

Further, when a polymer film satisfying the above properties is formed by polymerization, the polymerizable composition is
A monomer or oligomer having a reactive vinyl group,
Various polymerizable compounds of acrylate type and methacrylate type and a polymerization initiator, for example, Darocure 117 manufactured by Merck & Co.
3, 1116, and a mixture with commercially available products such as Nippon Kayaku Kayacure DETX can be used.

When the three-dimensional network structure is impregnated with the solution of the polymer compound, the viscosity of the solution is 300 cps or less, preferably 100 cps or less, for the purpose of forming a more uniform polymer film. Preferably 50 cps
It is used below. Also, as the solvent used,
It is appropriately selected depending on the polymer compound as a solute, and examples thereof include alcohols, ketones, esters, aromatic hydrocarbons, and water. The above polymer compound,
The polymerizable composition and the solvent may be used alone or in combination of two or more.

In the present invention, the polymer film incompatible with the liquid crystal to be impregnated has a three-dimensional network structure having a thickness of 0.2 to 2 μm.
The material is not particularly limited as long as it is formed with a thickness of. Further, when forming the polymer film, treatment such as heating, cooling, pressurizing, and depressurizing may be performed as necessary. After forming the polymer film, a washing treatment or a surface modification treatment may be performed as necessary. Is also good.

The liquid crystal 106 has a normal transmission
Nematic liquid crystal, cholesteric liquid crystal, smectic liquid crystal used alone in scattering mode liquid crystal display element,
Alternatively, a mixture thereof can be suitably used.

Further, as the spacer (not shown), a spacer having a substantially uniform particle size such as glass particles, plastic particles, and ceramic particles can be used. The particle size of the spacer is 1.0 to 50 μm, preferably 2.
Those having a range of 0 to 20 μm can be suitably used. 1.0
If it is less than μm, the scattering ability becomes insufficient as a transmission / scattering mode liquid crystal display element, and if it exceeds 50 μm, the transmittance becomes insufficient, which is not preferable.

In the present invention, the impregnation and injection of the liquid crystal may be performed under normal pressure or under reduced pressure, and can be easily performed by a capillary injection method.

In the liquid crystal display device obtained by the present invention, a thin film transistor or the like can be used as an electrode for applying an electric field. Further, when performing display control by heating the liquid crystal display element obtained in the present invention, a thermal head, a laser beam, or the like can be used. It is also possible to obtain a guest-photos type display element by mixing a dichroic dye in the liquid crystal.

The method for manufacturing a liquid crystal display device of the present invention can be widely applied to a transmission / scattering mode liquid crystal display device in which a three-dimensional network structure is impregnated with a liquid crystal, irrespective of a direct-view type or a projection type.

[0047]

The present invention will be specifically described below with reference to examples.

Example 1 An ITO electrode (thickness: 1000 mm) of 20 × 20 m was deposited.
A 1.1-mm-thick glass substrate having a m-square thickness is spin-coated with a methyl ethyl ketone (MEK) solution of an epoxy-based adhesive (Shalactbond EH-454NF; manufactured by Mitsui Toatsu Chemicals), and a 12 × 18 mm-thick film is formed thereon. A porous film (manufactured by Millipore) having a thickness of 125 μm, an average pore diameter of 10 μm, and a porosity of 85% was laminated, and bonded by heat curing.

Next, polystyrene (Mw = 28000)
0) Impregnated with a benzene solution and dried, and the porous film was polished with a grinder to a thickness of 10 μm. This was ultrasonically washed with benzene to remove polystyrene from the porous film to obtain a three-dimensional network structure. Observation with a scanning electron microscope of a similarly prepared product showed a diameter of 0.05 μm.
Many of the following fibrous stitches were observed.

Further, 0.5 wt% of polyacrylic acid (manufactured by Aldrich, Mw = 1,000,000) was added to the substrate.
After impregnating with a methanol solution, it was dried to obtain a polymer film. Observation of the three-dimensional network structure produced in the same manner with a scanning electron microscope revealed that the thickness of the film was 0.2 μm at the minimum and 2 μm at the maximum. FIG. 2A shows a scanning electron microscope photograph (5000 times) before the treatment, and FIG. 2B shows a scanning electron microscope photograph (5000 times) after the treatment.

The porous film side of the substrate is coated with an epoxy adhesive on a glass substrate on which an ITO electrode is deposited in the same manner as the above substrate, and a spacing control substance (glass fiber spacer; An epoxy-based adhesive in which a small amount of electric glass was added and dispersed was applied and bonded to the bonding side of this substrate to form a cell structure.

A liquid crystal (nematic liquid crystal E-37; manufactured by BDH) is adhered to the open end of the cell which is not sealed with an adhesive, and the liquid crystal is impregnated into the porous film by a capillary injection method under reduced pressure. Injected. Based on the weight of the cell before and after the impregnation, the impregnation ratio of the liquid crystal was 75%. ± 40 V, 60 Hz between the upper and lower substrates of the cell prepared as described above
When the rectangular wave was applied, the transmittance when the voltage was applied was 51
% And the contrast was 12: 1.

In this cell, the voltage was gradually increased from OV to ± 50 V, and further decreased from ± 50 V to OV, and the light transmittance was measured. As a result, almost no difference was observed. The hysteresis was as low as 8%.

Comparative Example 1 A porous film was laminated and bonded on a glass substrate on which an ITO electrode had been deposited, and was subjected to a grinder treatment in the same manner as in Example 1, except that the polymer film treatment was not performed. Similarly, a cell was created.

The cells prepared as described above have ± 40
When a rectangular wave of V and 60 Hz was applied, the transparency at the time of applying the voltage was 56%, but the contrast was 8: 1. Further, in the same manner as in the first embodiment, the cell was set to ± 50 from OV.
When the light transmittance is measured by increasing the voltage to V and further decreasing the voltage,
There was a difference in characteristics at the time of step-up and step-down. The hysteresis was as high as 25%.

Example 2 14 parts by weight of dipentaerythritol hexaacrylate (manufactured by Toa Gosei Chemical Co., Aronix M-402) and Kayacure DETX (manufactured by Nippon Kayaku) were placed between glass substrates on which ITO electrodes (thickness 1000 mm) were deposited. ) 0.2 parts by weight,
To a mixture of 0.2 parts by weight of Kayacure EPA (manufactured by Nippon Kayaku) and 86 parts by weight of nematic liquid crystal ZLI-2008 (manufactured by Merck), a small amount of glass fiber (manufactured by Nippon Glass) having an average particle size of 10 μm was added as a spacer. I held things.

Next, after irradiating ultraviolet rays with a high-pressure mercury lamp to cure the monomer component, the cell was immersed in a methanol solution and subjected to ultrasonic cleaning to remove the liquid crystal component to obtain a three-dimensional network structure. The above cell was treated with polyvinyl alcohol 0.1.
5 wt% aqueous solution (Nippon Gohsei, Gohsenol NH
-18), dried by heating and then washed with an appropriate amount of water to remove excess polyvinyl alcohol. Further, the cell was baked in an oven at 150 ° C. for 30 minutes.

When a rectangular wave of ± 20 V and 60 Hz was applied between the upper and lower substrates of the cell prepared as described above,
The transmittance when voltage is applied is 46%, and the contrast is
8: 1. When the voltage was gradually increased from OV to ± 30 V in this cell, and further decreased from ± 30 V to OV, and the light transmittance was measured, the hysteresis was as low as 18%.

Comparative Example 2 As in Example 2, 28 parts by weight of dipentaerythritol hexaacrylate (trade name: Aronix M-402, manufactured by Toa Gosei Chemical Co., Ltd.) and Kayacure DETX (Japan A mixture of 0.5 parts by weight of Kayaku EPA (manufactured by Kayaku), 0.5 parts by weight of Kayacure EPA (manufactured by Nippon Kayaku), and 71 parts by weight of nematic liquid crystal ZLI-2008 (manufactured by Merck) is mixed with a glass fiber having an average particle diameter of 10 μm as a spacer. (Manufactured by Nippon Glass Co., Ltd.) was added.

Next, the monomer component is cured with a high-pressure mercury lamp,
A cell in which the liquid crystal was dispersed and held in a three-dimensional network structure was formed by phase separation from the liquid crystal. When a voltage of ± 50 V from OV was applied to the upper and lower substrates of the cell, and the hysteresis was measured, it was as high as 34%.

[0061]

As described above , according to the present invention ,
Liquid crystal with good hysteresis, high light transmittance and high contrast by forming a polymer film on a three-dimensional network structure of a transmission / scattering mode liquid crystal display device in which a three-dimensional network structure is impregnated with liquid crystal. A display element can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal display device of the present invention .

FIG. 2 is a scanning micrograph showing the structure of the three-dimensional network structure of the present invention . FIG. 2 (a) is a three-dimensional network structure before forming a polymer film, and FIG. It is a three-dimensional network structure formed with a molecular film.

FIG. 3 is an explanatory diagram showing hysteresis characteristics in the present invention.

[Explanation of symbols]

 101, 101 'Substrate 102, 102' Electrode 103, 103 'Adhesive layer 104 Three-dimensional network structure 105 Polymer film 106 Liquid crystal

Continuing on the front page (72) Inventor Koichi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeo Eguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shunichi Onishi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-3-245121 (JP, A) JP-A-4-86807 (JP, A) JP-A-4-98220 (JP, A) JP-A-3-200927 (JP, A) JP-A-5-241136 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) G02F 1/1334 C09K 19/02

Claims (2)

(57) [Claims] 1. A liquid crystal display element having a three-dimensional network structure and a liquid crystal between a pair of substrates, at least one of which may have a transparent electrode, wherein the three-dimensional network structure is
Porosity with porosity of 80 to 98% made porous by stretching
Quality film, and the mesh surface of the three-dimensional network structure
A polymer film having a thickness of 0.2 to 2 [mu] m . 2. A method of manufacturing a liquid crystal display device having a three-dimensional network structure and a liquid crystal between at least one of a pair of substrates which may have a transparent electrode, wherein the three-dimensional network structure is provided. Forming a polymer film having a thickness of 0.2 to 2 [mu] m, and then injecting and impregnating a liquid crystal.