JPH05241137A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a ferroelectric liq. crystal display element having excellent insulating property and a large pretilt angle. CONSTITUTION:When two transparent electrode substrates 11a, 11b obtd. by successively forming transparent electrodes 12a, 12b and polyimide oriented films 15a, 15b on substrates are placed opposite to each other with the oriented films 15a, 15b inward and a ferroelectric liq. crystal 16 is sealed between them to obtain a liq. crystal display element, a first insulating layer 13a (13b) of Ta2O5 and a second insulating layer 14a (14b) of SiO2 or an org. polymer are successively formed on at least one of the transparent electrodes 12a, 12b.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, liquid crystal display elements used in clocks, computers, word processors, etc.
As its basic structure, it is usual that two transparent electrode substrates each having an alignment film provided on a transparent electrode are arranged with the alignment film inside, and a liquid crystal is sealed between them. The transparent electrode of such a liquid crystal display device is generally formed on the substrate in the form of a display pattern such as a stripe pattern or a grid pattern, and the alignment film is formed on the transparent electrode and the exposed substrate (other than the display pattern). Is provided by coating or vapor deposition. The two transparent electrode substrates are respectively arranged with the alignment film inside, and a ferroelectric liquid crystal is sealed between them to manufacture a liquid crystal display element. Therefore, the enclosed liquid crystal is generally in contact with only the alignment film. The alignment film is provided because it is necessary to align the liquid crystals in a certain direction, that is, to align the liquid crystals, and thereby the liquid crystal molecules are aligned.

The mainstream of such a liquid crystal display device is a display in a twisted nematic (TN) mode in which a nematic liquid crystal has a twisted structure. However, this TN type liquid crystal display element has a drawback that the response speed is slow and the limit is 20 milliseconds under the present circumstances, which is a big problem when it is used for a television panel or the like which requires high speed response. Is becoming

On the other hand, recently, a ferroelectric liquid crystal having a high-speed response has been expected and studied as a new field of display. Ferroelectric liquid crystals not only respond quickly to changes in the electric field, but also take one of the first optical stable state and the second optical stable state in response to the applied electric field, and It also has a property of maintaining the state when no voltage is applied, that is, a memory property (also called bistability). Therefore, in the liquid crystal display device using the ferroelectric liquid crystal, it is sufficient to apply the pulse voltage only when switching between the two states, so that the power supply and the electronic circuit for maintaining the optical state as in the past are not necessary. Therefore, the power consumption is reduced as compared with the conventional liquid crystal display element. That is, it can be said that the liquid crystal display element using the ferroelectric liquid crystal is a liquid crystal display element having a simple structure and realizing high-speed response.

For example, in a conventional ferroelectric liquid crystal display element (liquid crystal display panel) for a television panel, as described above, a transparent electrode substrate in which a transparent electrode and an alignment film are laminated in this order on a transparent substrate. The two sheets are arranged so that the alignment films face each other, and the ferroelectric liquid crystal is enclosed between them.
The transparent electrodes are each formed on the transparent substrate in the form of a striped display pattern.

In such a liquid crystal display device, in order to exhibit the high-speed response characteristic of the ferroelectric liquid crystal,
The distance (cell gap) between the transparent electrode substrates is extremely narrow, about 2 μm. Therefore, in the process of manufacturing the above-mentioned element, when conductive foreign matter (solid substance that prevents the formation of a cell gap) or dust is mixed in the liquid crystal, a short circuit occurs between the transparent electrodes, and even if a voltage is applied to the pixel. A potential difference cannot be obtained and display becomes difficult.

In order to prevent the above-mentioned problems, it is extremely difficult to eliminate foreign matters and dust from the viewpoint of manufacturing. JP-A-58-
Japanese Patent No. 172621 discloses a liquid crystal display element in which an insulating layer made of SiO ₂ is formed between the transparent electrode and the alignment film for the purpose of preventing a short circuit. The formation of such an insulating layer is effective for prevention of short circuit, but the above-mentioned memory property (bistability), which is the greatest feature of the ferroelectric liquid crystal, is deteriorated. When the insulating layer is made as thin as possible, the deterioration of the memory property is improved, but there is a problem that the insulating effect for preventing a short circuit becomes insufficient.

Japanese Unexamined Patent Publication (Kokai) No. 2-136827 discloses Ta ₂ O ₅ as an insulating layer material suitable for ferroelectric liquid crystals. Ta ₂ O ₅ has a large relative dielectric constant and an excellent insulating property, and is particularly effective when used in a ferroelectric liquid crystal display device having a large spontaneous polarization.

On the other hand, as an alignment film for a ferroelectric liquid crystal, an alignment film made of polyimide, which can obtain a large pretilt angle and easily obtain excellent switching characteristics and display characteristics such as bistability, is widely used. However, according to the study by the present inventor, when the polyimide alignment film is formed on the insulating layer of Ta ₂ O _5, a large pretilt angle cannot be obtained no matter what rubbing treatment is performed, and therefore, switching characteristics and bistable characteristics It has become clear that it is not possible to obtain a ferroelectric liquid crystal display element having sufficient performance in display characteristics such as properties.

[0010]

DISCLOSURE OF THE INVENTION The present inventor has found that Ta ₂ O
While maintaining the high insulating property of ₅ , while continuing to earnestly studied to obtain a ferroelectric liquid crystal display element having excellent display characteristics without impairing the excellent alignment characteristics of the polyimide alignment film formed thereon .. As a result, by interposing a thin film such as SiO ₂ between the Ta ₂ O ₅ insulating layer and the polyimide alignment film, it is possible to obtain a ferroelectric liquid crystal display element having excellent insulating properties and display characteristics. I found that.

Therefore, it is an object of the present invention to provide a ferroelectric liquid crystal display device which is excellent in insulation and exhibits a high pretilt angle. Another object of the present invention is to provide a ferroelectric liquid crystal display device which has excellent insulating properties and display characteristics such as switching characteristics and bistability.

[0012]

The above-mentioned object is to provide a substrate on
In a liquid crystal display element in which two transparent electrode substrates provided with a transparent electrode and a polyimide alignment film in this order are arranged with the alignment film inside, and a ferroelectric liquid crystal is sealed between them, at least one of Ta ₂ O ₅ on the transparent electrode
And a second insulating layer made of SiO ₂ or an organic polymer are formed in this order.

The preferred embodiments of the liquid crystal display device of the present invention are as follows.

1) The thickness of the first insulating layer is 30 to 300 n
The liquid crystal display device described above, wherein the liquid crystal display device is in the range of m.

2) The layer thickness of the first insulating layer is 50 to 250 n.
The liquid crystal display device described above, wherein the liquid crystal display device is in the range of m.

3) The liquid crystal display device, wherein the second insulating layer is made of SiO ₂ .

4) The liquid crystal display device, wherein the second insulating layer is made of an organic polymer.

5) The above liquid crystal display, wherein the organic polymer is at least one selected from the group consisting of polyamide, polyimide, polyimide amide, polyester, polyester imide, polysulfone, polyether sulfone and cross-linking acrylic resin. element.

6) The liquid crystal display device described above, wherein the layer thickness of the second insulating layer is 0.3 times or less the layer thickness of the first insulating layer.

7) The liquid crystal display device, wherein the transparent electrode is formed in a stripe shape.

[Structure of the Invention] The structure of the liquid crystal display device of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view of an example of the liquid crystal display element of the present invention. The transparent electrode 1 is formed on the transparent substrates 11a and 11b.
2a, 12b, first insulating layers 13a, 13b, second insulating layers 14a, 14b and polyimide alignment films 15a, 15b.
Are laminated in this order to form two transparent electrode substrates. The two transparent electrode substrates each have an alignment film 1
5a and 15b are arranged so as to face each other, and the ferroelectric liquid crystal 16 is enclosed between them. The first insulating layer is made of Ta ₂ O ₅ having a large relative dielectric constant and exhibits excellent insulating properties.
The second insulating layer provided on the first insulating layer is made of SiO ₂ or an organic polymer, is thinner than the first insulating layer, and is formed so as not to impair the alignment function (pretilt angle imparting function) of the polyimide alignment film. There is.

Although the insulating layers are provided on both transparent substrates in FIG. 1, only one of them may be provided. Even when both are provided, the effect of the present invention can be obtained if only one insulating layer has two layers. it can. The transparent electrode is formed on the transparent substrate in the form of a striped display pattern, but the insulating layer and the alignment film may be formed in the above pattern. The transparent electrodes 12a and 12b are both formed in a stripe shape, and at that time, the transparent electrode substrates are arranged so that the shapes of these stripes are orthogonal to each other. This allows matrix display. Further, the transparent electrode may be formed in a stripe shape only on one side.

FIG. 2 is a sectional view showing another example of the liquid crystal display element of the present invention. Transparent Substrate 2 Having Transparent Substrate 21a, Color Filter 27b, and Overcoat Layer 28b
1b on the transparent electrodes 22a, 22b, the first insulating layer 23
a, 23b, the second insulating layers 24a, 24b, and the polyimide alignment films 25a, 25b are laminated in this order to form two transparent electrode substrates. The two transparent electrode substrates are arranged so as to face the alignment films 25a and 25b, respectively, and the ferroelectric liquid crystal 26 is enclosed between them. 2 has the same configuration except that the color filter and the overcoat layer 28b are interposed between the one transparent substrate and the transparent electrode of FIG. The overcoat layer is
It is provided to protect the color filter layer, and may not be provided. By providing a color filter layer, color display is possible. Further, if desired, a black matrix may be interposed between the transparent electrode and the color filter transparent electrode.

As described above, the liquid crystal display device of the present invention prevents the upper and lower substrates from being short-circuited (electrical short-circuit) due to the high insulating function of the first insulating layer, while at the same time forming the Ta ₂ O ₅ insulating layer and the polyimide alignment film. By interposing a thin film such as SiO ₂ of the second insulating layer between the layers, the excellent alignment property of the polyimide alignment film (the function of giving a high pretilt angle) is secured, so that both the insulating property and the display property are obtained. Shows excellent characteristics.

The liquid crystal display device of the present invention is shown in FIGS.
In addition to those shown in FIG. 3, all the modes such as the use of spacers and the provision of polarizing plates, which are performed for ordinary liquid crystal display elements, are possible. In particular, it is preferable to use a spacer in order to secure a gap between both alignment films (that is, a layer thickness of the liquid crystal layer). As the spacer, glass fiber, glass beads, plastic beads, and metal oxide particles such as alumina and silica are used. The spacer particle size varies depending on the liquid crystal used, the alignment film material, the setting of the cell gap, the particles used as the spacer, etc., but is generally 1.0 μm to 5 μm.

As the transparent substrate, transparent electrode, ferroelectric liquid crystal and the like used in the liquid crystal display element of the present invention, all known materials conventionally used in ferroelectric liquid crystal display elements can be used.

Next, an example of manufacturing the liquid crystal display device of the present invention will be described below step by step. As the material of the transparent substrate,
Other than glass such as float glass with good smoothness, polyester such as polyethylene terephthalate and polybutylene terephthalate, epoxy resin, phenol resin, polyimide, polycarbonate, polysulfone, polyether sulfone, polyetherimide, acetyl cellulose, polyamino acid ester, aromatic Heat-resistant resins such as group polyamide, polystyrene, polyacrylic acid esters, polymethacrylic acid esters, vinyl-based polymers such as polyacrylamide, polyethylene, polypropylene, fluorine-containing resins such as polyvinylidene fluoride, and plastics formed from modified products thereof. A film can be mentioned.

As the transparent electrode, indium oxide (In
₂ O _3), it may be mentioned tin oxide (SnO ₂₎ and ITO (indium tin oxide) or the like. The transparent electrode is formed on the substrate in a stripe shape or a grid shape.

The insulating layer of the present invention comprises the first insulating layer and the second insulating layer as described above, and the first insulating layer is Ta ₂ O.
The film of No. ₅ and the second insulating layer is a film of SiO ₂ or an organic polymer. Examples of the organic polymer material include polyamide (nylon), polyimide, polyimide amide, polyester, polyester imide, polysulfone, polyether sulfone, and crosslinked acrylic resin. As the second insulating layer, a film made of SiO ₂ is preferable because a high pretilt angle can be easily obtained. The thickness of the first insulating layer is 3
It is preferably in the range of 0 to 500 nm, and further 5
The range of 0 to 300 nm is preferable. The thickness of the second insulating layer is preferably 0.3 times or less the layer thickness of the first insulating layer, and 0.2
It is preferably double or less. The layer thickness of the second insulating layer is 10 to 1
It is preferably in the range of 00 nm.

The insulating layer of Ta ₂ O ₅ and SiO ₂ is formed by a conventional method of forming an inorganic compound such as a vacuum evaporation method by resistance heating, a vacuum evaporation method by electron beam (EB) heating, and a sputtering method. The ion plating method or the like can be used.

The second insulating layer of the organic polymer is, for example, a polymer of the above polyamide (nylon), polyester, polysulfone or polyethersulfone, or a precursor thereof in the case of a crosslinkable acrylic resin or polyimide. The second insulating layer can be formed by dissolving the solvent in a solvent to prepare a coating solution, applying the solution onto the first insulating layer of the transparent substrate with a spin coater, drying, and optionally heat treating it.

The alignment film of the present invention is a polyimide thin film. The polyimide may be not only polyimide that has been conventionally used as an alignment film, but also any polyimide that can be used as an alignment film. To form the polyimide alignment film, a solution is prepared by dissolving polyimide and / or its precursor polyamic acid in an appropriate solvent such as N-methyl-2-pyrrolidone, dioxane, THF, or a glycol derivative. In addition to the above components, the coating liquid may contain other high molecular weight polymers or organometals as sub-components for the purpose of increasing the adhesion to the substrate or adjusting the viscosity of the coating liquid. Good.

The alignment film can be formed by applying the coating liquid for forming an alignment film on the insulating layer of the present invention by a spin coater, drying and heat treatment.

The layer thickness of the alignment film is generally 20 to 100.
It is 0 nm, preferably 30 to 500 nm.

The coating film provided on the insulating layer or the transparent electrode substrate is heat-treated and then rubbed with a synthetic fiber such as nylon, polyester or polyacrylonitrile, or a natural fiber such as cotton or wool. To be done.

Further, as the ferroelectric liquid crystal used in the present invention, a conventionally known one can be used.

The liquid crystal having ferroelectricity is specifically a chiral smectic C phase (SmC ^* ) or H phase (SmH
^* ), I phase (SmI ^* ), J phase (SmJ ^* ), K phase (S
mK ^* ), a G phase (SmG ^* ) or an F phase (SmF ^* ).

The ferroelectric liquid crystals that can be used in the present invention are exemplified below.

[0040]

[Chemical 1] (R is an n-alkyl group or an n-alkoxy group, m = 5
-10, 12, 14)

[0041]

[Chemical 2] (R is an n-alkyl group or an n-alkoxy group, m = 5
-10, 12, 14)

[0042]

[Chemical 3] (R is an n-alkyl group or an n-alkoxy group, m = 5
-10, 12, 14)

[0043]

[Chemical 4] (R is an n-alkyl group or an n-alkoxy group, m = 5
In addition to the above, for example, the following can be mentioned.

[0044]

[Chemical 5]

[0045]

[Chemical 6] (Where R = CH ₃ , C ₂ H ₅ )

[0046]

[Chemical 7]

[0047]

[Chemical 8]

[0048]

[Chemical 9]

[0049]

[Chemical 10]

[0050]

[Chemical 11]

[0051]

[Chemical 12]

[0052]

[Chemical 13]

[0053]

[Chemical 14]

[0054]

[Chemical 15]

In addition to the above, all known ferroelectric liquid crystals described in, for example, "High-speed liquid crystal technology" (published by CMC) p. 127-161 can be used in the present invention.

Specific liquid crystal compositions include CS-1018, CS-1023 and CS- manufactured by Chisso Corporation.
1025, CS-1026, DO manufactured by Roddick Co., Ltd.
F0004, DOF0006, DOF0008, ZLI-4237-000, ZLI-4237- manufactured by Merck & Co., Inc.
100, ZLI-4654-100, and the like, but are not limited thereto. There is no problem even if a dichroic dye, a viscosity reducing agent, or the like which dissolves in the liquid crystal is added to these liquid crystals.

A pair of transparent electrode substrates having the transparent substrate, the transparent electrode, the insulating layer and the alignment film, which are manufactured as described above, are provided on at least one side so that the alignment film is on the inside. Open it and let it face each other to make a cell. The size of this gap, that is, the cell gap is 1μ.
It is generally about m to 6 μm. Next, a ferroelectric liquid crystal is injected into this cell, sealed, and then gradually cooled.

The liquid crystal display device of the present invention can be manufactured as described above. Of course, the liquid crystal display element of the present invention, a polarizing plate, a reflection plate, a retardation plate, depending on the purpose of use,
A structure such as a color filter that is provided in a conventional liquid crystal display element can be provided.

Next, examples and comparative examples of the present invention will be described.
However, the present invention is not limited to this embodiment.

[0060]

【Example】

[Example 1] Transparent electrodes of indium-tin oxide (ITO) were formed in stripes (electrode width: 200 μm, on each of two 1.1 mm-thick glass plates by an ordinary photoresist method). Gap between electrodes: 15 μm)
Formed.

Ta ₂ O ₅ was vacuum-deposited on the electrode-bearing surface of the _two glass plates with ITO electrodes to provide a first insulating layer having a layer thickness of 120 nm. (Vacuum deposition conditions) Degree of vacuum: 1 × 10 ^-5 Torr Substrate heating temperature: 200 ° C. Deposition rate: 7Å / sec

SiO ₂ was vacuum-deposited on the first insulating layer under the following conditions to form a second insulating layer having a layer thickness of 20 nm. (Vacuum deposition conditions) Degree of vacuum: 1 × 10 ⁻⁵ Torr Substrate heating temperature: 200 ° C. Deposition rate: 5Å / sec

On the second insulating layer, the following diamine compound:

[0065]

[Chemical 16] And the following tetracarboxylic dianhydride:

[0066]

[Chemical 17] The following polyamic acid obtained by reaction with:

[0067]

[Chemical 18] 3 parts by weight was dissolved in 97 parts by weight of N, N-dimethylacetamide and the coating solution was applied by a spinner.

The condition of the spinner is 2500 rpm.
m., time 30 seconds. After coating, it was dried at 280 ° C. for 1 hour to form a polyimide alignment film.

Both surfaces of this coating film were rubbed with a nylon brushed cloth, and the two rubbing surfaces were placed inside, and two glass plates were 3 μm thick so that the rubbing directions were the same and the electrode patterns were orthogonal. And a cell gap having a cell gap of 3 μm was produced by stacking the cells through the spacers.
Ferroelectric liquid crystal ZLI-2293 manufactured by Merck
Was injected at 100 ° C. and gradually cooled to room temperature at a rate of about 2 ° C./minute to manufacture a liquid crystal display element.

[Comparative Example 1] In Example 1, except that the second insulating layer of SiO ₂ was not formed on the first insulating layer.
A liquid crystal display device was manufactured in the same manner as in Example 1.

Comparative Example 2 In Example 1, the SiO ₂ layer of the second insulating layer was formed as the first insulating layer on the transparent electrode, and the Ta ₂ O ₅ layer of the first insulating layer was used as the second insulating layer. S as a layer
A liquid crystal display device was manufactured in the same manner as in Example 1 except that the liquid crystal display device was formed on the iO ₂ layer (first insulating layer).

[Embodiment 2] In Embodiment 1, polyimide (L
A liquid crystal display element was manufactured in the same manner as in Example 1 except that X-5400, manufactured by Hitachi Chemical Co., Ltd., was applied and dried under the following conditions. Spinner conditions are 2500 rpm.
After coating, it was dried at 280 ° C. for 30 minutes.

[Comparative Example 3] In Example 2, except that the second insulating layer of SiO ₂ was not formed on the first insulating layer.
A liquid crystal display device was manufactured in the same manner as in Example 2.

Example 3 In Example 1, polyamide (nylon 12) was used as the second insulating layer instead of SiO _2.
A liquid crystal display element was manufactured in the same manner as in Example 1 except that the second insulating layer was formed by applying and drying the above-mentioned m-cresol (3% by weight solution). Spinner conditions are 2500 rpm for 30 seconds and 20 after application.
It was dried at 0 ° C. for 1 hour.

[Evaluation of Liquid Crystal Display Element] 1) Pretilt Angle The liquid crystal display elements obtained in Examples 1 to 3 and Comparative Examples 1 to 3 as described above were analyzed using a polarizing microscope manufactured by Nikon Corporation. The pretilt angle was measured by the crystal rotation method.

2) Insulating property On the insulating layer of the above-mentioned substrate with an insulating layer of the liquid crystal display element obtained as described above, one side has a contact area of 1 cm ² with the insulating layer.
The conductive rubber of the electrode having the conductive rubber is strongly adhered vertically. The electrical resistance was measured in this dry state.

The measurement results are shown in Table 1.

[0078]

[Table 1] Table 1 ──────────────────────────────── Pretilt angle Insulation (electrical resistance) ──── ──────────────────────────── Example 1 10 ° 5 × 10 ⁶ Ω or more Comparative Example 1 4 ° 5 × 10 ⁶ Ω or more Comparative Example 2 5 ° 5 × 10 ⁶ Ω or more ───────────────────────────────── Example 2 17 ° 5 × 10 ⁶ Ω or more Comparative Example 3 7 ° 5 × 10 ⁶ Ω or more ───────────────────────────────── Example 3 11 ° 5 × 10 ⁶ Ω or more ────────────────────────────────

As is clear from Table 1, the liquid crystal display devices of Examples 1 to 3 have a high pretilt angle and are excellent in display characteristics such as switching characteristics and bistability. Also, it can be seen that the electric resistance is high and the insulating property is excellent.

[0080]

The liquid crystal display device of the present invention comprises _two insulating layers of a first insulating layer of Ta ₂ O _{5 and} a second insulating layer of SiO ₂ or an organic polymer on the surface of a transparent electrode such as a striped electrode. Are formed. That is, the high insulating function of the Ta ₂ O ₅ film (first insulating layer) prevents short circuit (electrical short circuit) between the upper and lower substrates, and the SiO ₂ film is formed between the Ta ₂ O ₅ insulating layer and the polyimide alignment film. By interposing the thin film of 1), excellent alignment characteristics (function of giving a high pretilt angle) of the polyimide alignment film are secured. As a result, the liquid crystal display device of the present invention exhibits excellent characteristics in both insulation and display characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a configuration example of a liquid crystal display element of the present invention.

FIG. 2 is a cross-sectional view schematically showing another configuration example of the liquid crystal display element of the present invention.

[Explanation of symbols]

 11a, 11b, 21a, 21b Transparent substrate 12a, 12b, 22a, 22b Transparent electrode 13a, 13b, 23a, 23b First insulating layer 14a, 134, 24a, 24b Second insulating layer 15a, 154, 25a, 25b Alignment film 16 , 26 Liquid crystal 27b Color filter 28b Overcoat layer

Claims (1)

[Claims] 1. A transparent electrode substrate having a transparent electrode and a polyimide alignment film provided in this order on a substrate, with the alignment film inside, and arranging a ferroelectric liquid crystal between them. In the liquid crystal display element, the first insulating layer made of Ta ₂ O ₅ and the _second insulating layer made of SiO ₂ or an organic polymer are formed in this order on at least one transparent electrode. Liquid crystal display device.