JP2001290150A - Liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal element having high visual field angle characteristics, high contrast, high response speed, high accuracy and high productivity. SOLUTION: The liquid crystal element is formed with a liquid crystal layer 1 consisting of a discotic liquid crystal having both an edge-on alignment and a uniaxial alignment between two substrates 2a and 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device which can be used for a light valve used in a flat panel display, a projection display, a printer, and the like. The present invention also relates to a phase compensator, a viewing angle compensator, a liquid crystal switching element, an active liquid crystal element, and a liquid crystal device using the liquid crystal element.

[0002]

2. Description of the Related Art A CRT is known as the most widely used display. It is widely used as a moving image output for televisions and VTRs, or as a monitor for personal computers. However CRT
Due to its characteristics, flicker and scanning fringes due to lack of resolution may lower visibility of a still image, or may cause deterioration of a phosphor due to burn-in. Recently, C
There are also concerns about the effects of electromagnetic waves generated by RT. Since the CRT must have a large volume behind the screen due to its structure, it hinders the convenience of information equipment and is not suitable for saving space in offices and homes.

As a solution to such a disadvantage of the CRT, there is a liquid crystal display element. See, for example, M. Schadt and W. Helfrich, Applied Physics Le.
Vol. 18, No. 4 (February 15, 1971)
Twisted nematic shown on pages 127-128.
c) One using liquid crystal is known. In addition, in-plane switching mode called IPS, multi-domain vertical alignment mode called MVA, FLC, AFL
A high-speed switching mode of a smectic liquid crystal called C is known.

In recent years, a liquid crystal element called a TFT using this type of liquid crystal has been developed and commercialized. In this type, a transistor is formed for each pixel, there is no problem of crosstalk, and 10 to 13 inch class displays are being manufactured with good productivity due to rapid progress of production technology in recent years. is there. However, there are still problems in productivity, liquid crystal response speed, and viewing angle in terms of making a larger size with a good viewing angle, and a frame frequency of 60 Hz or more, in which moving images can be reproduced without any problem.

[0005] Such technical problems are the viscosity of the liquid crystal material,
Due to its elasticity or optical birefringence and its use, expectations for new liquid crystal materials, alignment states, and new switching modes are endless.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above prior art, and has as its object to provide good viewing angle characteristics, high contrast, high speed response, high definition, and high productivity. It is intended to provide a liquid crystal element.

[0007]

That is, the present invention is a liquid crystal element characterized in that the discotic liquid crystal has an edge-on orientation and uniaxiality.

[0008] The discotic liquid crystal may be arranged between two substrates. Preferably, the discotic liquid crystal is in a nematic discotic phase. The liquid crystal phase may be a nematic discotic phase containing a rod-like liquid crystal. The discotic liquid crystal may be subjected to electric field switching.

Further, the present invention is a phase compensator or a viewing angle compensator comprising the above-mentioned liquid crystal element. Further, the present invention is a liquid crystal switching element including the above-mentioned phase compensator or viewing angle compensator. Further, the present invention is an active liquid crystal device comprising the above liquid crystal device. Further, the present invention is a liquid crystal device using the above liquid crystal element.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies, the present inventors have found that the alignment state of a discotic liquid crystal is edge-on.
In addition, a liquid crystal element having uniaxiality can improve the viewing angle of a nematic liquid crystal element or the like as a viewing angle compensation film, and on the other hand, can provide a new liquid crystal element such as a wide viewing angle liquid crystal element that switches itself. Headings,
The present invention has been completed.

That is, the present invention relates to a liquid crystal element in which the alignment state of the discotic liquid crystal is edge-on and uniaxial, and a new liquid crystal element utilizing the alignment state. This is the liquid crystal device used.

First, a liquid crystal element in which the discotic liquid crystal has an edge-on and uniaxial property, which is the first invention of the present invention, will be described.

With respect to the state of orientation of the discotic liquid crystal, it is well known that the plate portion of the discotic liquid crystal is oriented parallel to the substrate, which is called side-on orientation. Further, a hybrid alignment state as described in JP-A-9-212444 is also known. On the other hand, an orientation state called edge-on orientation is known, which is an orientation state in which the plate stands perpendicular to the substrate. The edge-on orientation can be usually obtained by using an orientation film having a vertical orientation on the substrate, but the method of turning the dish, that is, the discotic director has not been uniformly controlled in the uniaxial orientation. Edge-on is obtained by weakening the interaction of discotic liquid crystal with the interface, which is difficult to align compared to the rod-shaped liquid crystal.
The reason is considered to be technical difficulties that balance the contradiction of the orientation and the uniaxial orientation obtained by strengthening the interaction with the interface.

The inventor of the present invention has been able to realize a state in which the discotic liquid crystal has an edge-on and uniaxial state while diligently studying the liquid crystal material, the alignment film material, the preparation conditions and the like. Figure 1 shows the edge of a discotic liquid crystal.
It is a schematic diagram which shows -on and uniaxial orientation. FIG. 1 (a) is a view of a discotic (plate) viewed from the front, and FIG.
(B) shows the discotic (plate) seen from the side.

Hereinafter, the liquid crystal device of the present invention will be specifically described. As the discotic liquid crystal used in the present invention, a discotic columnar phase, a nematic discotic phase, or the like can be used, but the nematic discotic phase is preferably used because it has relatively high fluidity and is easy to control the alignment. Specific examples include compounds having the following structures and liquid crystal compositions containing them.

[0016]

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[0017]

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[0018]

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[0019]

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[0020]

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[0021]

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[0022]

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[0023]

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[0024]

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[0025]

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[0026]

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The discotic liquid crystal used includes an ultraviolet absorber, a radical trapping agent, an antioxidant, a viscosity reducing agent,
Nematic liquid crystals, smectic liquid crystals and the like may be contained.

Next, an alignment control method will be described while describing a specific example of a liquid crystal element. FIG. 2 is a schematic sectional view showing one example of the liquid crystal element of the present invention. In FIG. 2, reference numeral 1 denotes a liquid crystal layer made of a liquid crystal composition, 2a and 2b denote substrates, and glass, plastic, or the like is used. 3a, 3b
Is a transparent electrode such as ITO. 4a and 4b are orientation control layers, and an edge-on uniaxial orientation control layer is required on at least one substrate. As a method of forming the edge-on uniaxial orientation control layer, for example, by evaporation or sputtering, silicon monoxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron A method of forming an inorganic substance such as a nitride from an oblique direction, polyvinyl alcohol, polyimide, polyimide amide, polyester, polyamide, polyester imide, polyparaxylene, polycarbonate, polyvinyl acetal, polyvinyl chloride, polystyrene,
There is a method of forming a film using an organic substance such as polysiloxane, cellulose resin, melamine resin, urea resin, and acrylic resin, and then rubbing (rubbing) the surface with a fibrous material such as velvet cloth or paper. In addition, it is also possible to provide a short prevention layer.

In particular, it is preferable to use a polyimide rubbing film as the uniaxially oriented layer in order to obtain better edge-on uniaxial orientation. Usually, polyimide is obtained by coating a film in the form of polyamic acid and baking it. Polyamic acid is excellent in productivity because it is easily soluble in a solvent. Recently, polyimides soluble in solvents have also been produced, and such polyimides are desirable from the viewpoint of voltage holding ratio. Polyimides are preferably used from the viewpoint of obtaining better uniaxial orientation and having high productivity even in view of such technical progress. More preferable polyimide is a polyimide in which ordinary rod-shaped liquid crystal is vertically aligned without rubbing, and it is preferable to rub such polyimide relatively strongly.

Reference numeral 5 denotes a sealing material, and an adhesive such as Stract Bond (registered trademark) is used. Usually, a spacer is used in the liquid crystal layer to control the cell thickness, for example, silica beads or the like are used.
Reference numeral 6 denotes a backlight light source. Reference numeral 8 denotes a polarizing plate, which is usually arranged in crossed Nicols.

Next, a second liquid crystal device utilizing the edge-on uniaxial alignment state of the discotic liquid crystal, which is the second invention of the present invention, will be described.

One example is the edg of discotic liquid crystal.
A phase compensator and a viewing angle compensator utilizing an e-on uniaxial orientation state. Discotic liquid crystal e shown in FIG.
The dge-on uniaxial orientation has a refractive index anisotropy complementary to the orientation state of the rod-shaped liquid crystal 11 shown in FIG. 3, and can provide a liquid crystal display device having a very excellent wide viewing angle. Particularly, in the in-plane switching type rod-shaped liquid crystal element, the complementary matching is excellent. Examples of the in-plane switching type liquid crystal element include a so-called IPS element and an FFS element using a nematic liquid crystal, and an FLC and an AFLC element using a smectic liquid crystal. These liquid crystal elements may be both passive elements and active elements.

FIG. 4 is a schematic view showing an optical relationship among a liquid crystal, a polarizing plate, and a polymer liquid crystal retardation plate. In FIG. 4, the optical axes of the upper and lower polarizing plates 12a and 12b are in a vertical relationship. When used as a phase compensator or viewing angle compensator in this way,
The discotic liquid crystal in the present invention is desirably a polymer from the viewpoint of environmental resistance. As a method of polymerizing, a method of forming an alignment state as shown in FIG. 1 using a polymerizable discotic liquid crystal, and then polymerizing and fixing the alignment by photopolymerization is preferably used. Of course, it can also be obtained by controlling the alignment of a polymer discotic liquid crystal.

Further, a liquid crystal element using the discotic liquid crystal in the present invention as a switching liquid crystal is also possible. One stable state is an edge-on uniaxial orientation state,
Switching to de-on orientation state, edge-on
Switching to the non-axial orientation state, or edge
-On phase shift switching between different phases although in a uniaxial orientation state. Switching by dielectric anisotropy torque is possible by applying an electric field, and it is possible to turn on and off by using a polarizing plate. Regarding the electric field responsiveness of discotic liquid crystal, when the electric field strength is increased, the discotic liquid crystal plate switches to a more upright position (director sleeps) when the electric field intensity is increased. Become. The opposite is true for positive dielectric anisotropy. It is also possible to add a nematic liquid crystal or a smectic liquid crystal to further increase the dielectric anisotropy. Such a liquid crystal element is
An excellent liquid crystal switching element having characteristics of high-speed response and a wide viewing angle can be provided.

The liquid crystal element of the present invention using a discotic liquid crystal as a switching liquid crystal is not limited to the above example.

The liquid crystal device of the present invention described above can be used together with an active device. For example, an active matrix element shown in FIG. 5 using the configuration described above as one pixel is exemplified. In FIG. 5, a pair of transparent substrates (eg, glass substrates) 41, 4
Among them, on the lower substrate 41, a transparent pixel electrode 43 and an active element 44 connected to the pixel electrode 43 are formed in a matrix. The active element 44 is, for example, T
It is composed of a thin film transistor called FT. As the transistor, a semiconductor such as an amorphous silicon base, a polysilicon type, a μ crystal base, or a single crystal silicon can be used. In this example, reference numeral 44 denotes a TFT. 44 includes a gate electrode formed on the substrate 41, a gate insulating film covering the gate electrode, a semiconductor layer formed on the gate insulating film, and a source electrode and a drain electrode formed on the semiconductor layer. .

Further, on the lower substrate 41, gate lines (scan lines) 45 are arranged between the rows of the pixel electrodes 43 as shown in FIG. 6, and information signal lines 46 are arranged between the columns of the pixel electrodes 43. The gate electrode of each TFT 44 is connected to a corresponding gate line 45, and the drain electrode is connected to a corresponding information signal line 46. Gate line 4
5 is connected to a row driver via an end 45a, and the information signal line 46 is connected to a column driver via an end 46a. The row driver scans the gate line 45 by applying a gate signal. The column driver applies a signal corresponding to the display data. The gate line 45 is covered with the gate insulating film of the TFT 44 except for the end 45a, and the information signal line 46 is formed on the gate insulating film. The pixel electrode 43 is formed on the gate insulating film, and has one end connected to the source electrode of the TFT 44. Further, a transparent electrode 47 facing each pixel electrode 43 of the lower substrate 41 is formed on the upper substrate 42 in FIG. The counter electrode 47 is composed of one electrode having an area covering the entire display area, and a reference voltage is applied thereto. The transmittance changes according to the information signal voltage, and gradation expression can be performed. In addition, a capacitor serving as an auxiliary capacitance is often arranged for each pixel.

Such a matrix element is used in a transmission type or in a reflection type. If it is transparent,
Usually a light source is used. In the case of reflection, a reflective layer is formed in the device. Further, the present invention is applied to both a direct view type and a projection type. It can also be used as a light valve for a printer or the like.

The liquid crystal element of the present invention constitutes a liquid crystal device having various functions. As an example, the liquid crystal element is used in a display panel section and provided with a driving circuit, a backlight, a light diffusion plate and the like. A display device may be used.

[0040]

Next, the present invention will be described more specifically with reference to examples and comparative examples. Note that the present invention is not limited to these examples.

Example 1 A discotic liquid crystal A having the following structure was used.

[0042]

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A represents that the molar ratio of R ₁ / R ₂ is 5/1 and 4 /
What is 2 and 3/3 is a mixture of 22:59:16. The phase transition of A is discotic rectangular phase- (131 ° C.)-Nematic discotic phase- (2
00 ° C.)-Iso (heating process).

Preparation of Cell> Cell α, α * Two glass substrates having a thickness of 1.1 mm were prepared, and an ITO film having a thickness of about 70 nm was formed as a transparent electrode.

A 4 wt% solution of polyimide JALS 2022 manufactured by Nippon Synthetic Rubber Co., Ltd. was applied to both substrates at 500 rpm for 5 seconds for the first time and 1500 rpm for the second time.
m for 30 seconds.

After that, pre-drying was performed at 80 ° C. for 2 minutes, and then heat baking was performed at 200 ° C. for 1 hour. Rubbing was performed using a cotton nonwoven fabric at a position where 1.2 mm cotton was pushed in at 1,000 rotations.

An IPA solution in which resin beads having an average particle diameter of 10 μm are dispersed at 0.01% by weight is spin-coated on the surface of one of the substrates under the conditions of 1500 rpm and 10 sec, and the bead spacer is set to a dispersion density of about 100 / mm ^2. Was sprayed. A thermosetting liquid adhesive was applied to the substrate by a printing method.

The resulting two substrates were rubbed and bonded together with their rubbing axes aligned and heated and cured in an oven at 150 ° C. for 90 minutes to obtain a cell α. A cell α * not rubbed was prepared in the same manner as described above.

The discotic liquid crystal A is injected into the cell α in an isotropic phase, and gradually cooled from 210 ° C. at 2 ° C./min.
° C, a uniform orientation state with strong uniaxial birefringence was observed under a polarizing microscope, and the edge-on was uniform.
It was confirmed that the film was uniaxially oriented.

Example 2 The liquid crystal A of Example 1 was replaced with a nematic liquid crystal KN manufactured by Chisso Corporation.
The liquid crystal composition B was prepared by mixing 5030 with 25 wt%. This liquid crystal composition B was injected into the cell α, and slowly cooled and aligned in the same manner as in Example 1. The liquid crystal composition B was transferred from about 60 ° C. to an Nd phase (nematic discotic phase), and was uniaxially heated at 50 ° C. under a polarizing microscope. A uniform alignment state with strong birefringence was observed, and it was confirmed that the edge-on uniaxially aligned.

Example 3 The liquid crystal composition B used in Example 2 was manufactured by Ciba Geigy, Inc.
A mixture containing 1 wt% of Irgacure 184 as a photopolymerization initiator was poured into the cell α in the same manner as in Example 2, and then gradually cooled to 50 ° C.
When held in the same manner as in Example 2, under a polarizing microscope,
Uniform orientation with strong uniaxial birefringence is observed,
It was confirmed that the edge-on was uniaxially oriented uniformly.

In this state, exposure was performed for 5 minutes with ultraviolet rays having a center wavelength of 365 nm at about 12 mW / cm ² , and a uniform edge was obtained.
The -on uniaxial orientation was fixed. Although the temperature was raised to 120 ° C., the alignment state was maintained.

An electric field was applied to a ferroelectric liquid crystal cell, which was an in-plane switching liquid crystal, so that it was uniformly aligned in one uniform direction, the polarizing plate was positioned at a cross Nicol position, and arranged in a dark state. An electric field was again applied to this, and the uniform was made uniform in the direction of the other uniform, thereby obtaining a bright state in which the maximum luminance could be obtained. In this state, the retardation of the liquid crystal cell was 200 nm, and the transmittance with respect to the empty cell state was 74% in paranicol. When the viewing angle of this cell was changed in the major axis direction of the liquid crystal, the bluish color was sharply colored from an angle of 50 degrees. However, when the discotic liquid crystal element was placed above, the bluish color was improved. Was.

Example 4 An AC electric field of 10 V and 60 Hz was applied to the liquid crystal device of Example 2 to obtain a dark field under a polarizing microscope. Using this, a single crystal silicon transistor (with an on-resistance of 50
Ω) and 2 nF ceramic capacitors to form active elements. When a gate signal having a selection period of 30 μS was applied thereto and a plus 6 V electric field was applied from the information signal line, light modulated under a microscope was observed.

[0055]

As described above, the liquid crystal device of the present invention has the effect of realizing a liquid crystal device and a display device with high viewing angle characteristics, high contrast, high speed response, high definition and high productivity. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing edge-on and uniaxial orientation of a discotic liquid crystal.

FIG. 2 is a schematic sectional view showing one example of the liquid crystal element of the present invention.

FIG. 3 is a schematic view showing an alignment state of a rod-shaped liquid crystal.

FIG. 4 is a schematic diagram showing an optical relationship among a liquid crystal, a polarizing plate, and a polymer liquid crystal retardation plate.

FIG. 5 is a schematic diagram illustrating an example of an active matrix element.

FIG. 6 is a schematic diagram illustrating an example of an active matrix element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal layer 2a, 2b Substrate 3a, 3b Transparent electrode 4a, 4b Alignment control layer 5 Seal material 6 Backlight light source 8 Polarizer 10 Plate 11 Bar-shaped liquid crystal 12a, 12b Polarizer 13 Refractive index ellipsoid of polymer discotic liquid crystal 14 Index Ellipsoid of Bar-shaped Liquid Crystal 15a, 15b Substrate 18 Alignment Film 19 Alignment Film 20 Sealant 21 Liquid Crystal 22 Spacer Bead 23 Protective Plate 24 Protective Plate 31 Row Driver 32 Column Driver 41 Lower Transparent Substrate 42 Upper Transparent Substrate 43 Pixel Electrode 44 Active element (TFT) 45 Gate line (scanning line) 46 Data line (gradation signal line) 47 Counter electrode

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/13363 G02F 1/13363 1/137 1/137 F-term (Reference) 2H049 BA02 BA06 BA46 BC04 BC05 BC22 2H088 EA02 EA47 GA01 GA02 HA03 HA08 MA01 MA07 2H090 HB07Y HB08Y HB16Y HC05 HC08 LA06 MA01 MB01 MB06 2H091 FA11X FA11Z GA06 GA11 GA13 LA16 LA19 4H027 BA08 BD08 BD20 BD21 DM03

Claims (10)

[Claims] An alignment state of a discotic liquid crystal is ed.
A liquid crystal element having a geo-on property and a uniaxial property. 2. The liquid crystal device according to claim 1, wherein the discotic liquid crystal is disposed between two substrates. 3. The liquid crystal device according to claim 1, wherein the discotic liquid crystal has a nematic discotic phase. 4. The liquid crystal device according to claim 3, wherein the liquid crystal phase is a nematic discotic phase containing a rod-like liquid crystal. 5. The liquid crystal device according to claim 1, wherein electric field switching of the discotic liquid crystal is performed. 6. A phase compensator comprising the liquid crystal element according to claim 1. 7. A viewing angle compensator comprising the liquid crystal element according to claim 1. 8. A liquid crystal switching element comprising the phase compensator or the viewing angle compensator according to claim 6. 9. An active liquid crystal device comprising the liquid crystal device according to claim 1. 10. A liquid crystal device using the liquid crystal element according to claim 1.