JP2006178016A - Liquid crystal display element and manufacturing method thereof - Google Patents

Abstract

A liquid crystal display element including a substrate having an alignment film made of an inorganic material that can be easily formed and a method for manufacturing the same are provided.
A substrate having an alignment film formed by applying an alignment treatment after a coating film composed of SiOx having an alkyl group in a side chain is applied. The alignment process is any one of rubbing process, optical alignment process, and beam process. A vertical alignment type liquid crystal having a refractive index of 0.10 to 0.20 and negative dielectric anisotropy is filled between two substrates on which alignment films are formed, and the distance between the substrates is set to 3.0 μm or less. Driving is performed by a one-field inversion driving method in which the applied voltage is inverted every field.
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Description

  The present invention relates to a liquid crystal display element and a method for manufacturing the same.

  Conventionally, in a projection-type liquid crystal display device that displays a predetermined image by irradiating light emitted from a light source onto a liquid crystal display element, a high-luminance image is required. It is desirable to use a liquid crystal display element having a high transmittance using a TN (Twisted Nematic) type liquid crystal.

  However, in such a projection-type liquid crystal display device, the liquid crystal display element is exposed to a high temperature of a maximum of 60 to 65 ° C. with long-term use, and therefore an organic material that is an alignment film material of the liquid crystal display element is used. It is easy to deteriorate and there was a limit to extending the service life.

  Therefore, attempts have been made to improve light resistance by forming an alignment film with an inorganic material instead of an organic material.

  In such an attempt, when an inorganic alignment film is used for a liquid crystal display element using a TN liquid crystal, the chemical interaction between the inorganic alignment film and the liquid crystal is weak. Even if such an alignment treatment was performed, the alignment stability was low and it could not be put to practical use. However, when a vertically aligned liquid crystal was used, it was aligned vertically without the need for alignment restriction as in the TN type. The present inventors have found that a relatively stable vertical alignment state can be obtained by an alignment film to be formed and a shape effect.

  Accordingly, the present inventors have invented a liquid crystal display element using a silicon oxide film made of silicon oxide, which is an inorganic material, as an alignment film (see, for example, Patent Document 1).

  The alignment film of this liquid crystal display element is formed by applying an inorganic coating material having an alkyl group on the side chain onto a predetermined substrate and baking it, and then inclining SiOx from the oblique direction with respect to the normal direction of the substrate. It is formed by vapor deposition.

Then, the TFT substrate on which the alignment film is formed in this way and the counter substrate are arranged so as to oppose each other, and a vertically aligned liquid crystal is filled between the TFT (Thin Film Transistor) substrate and the counter substrate so that the liquid crystal display element Is forming.
JP 2004-126463 A

  However, the formation of the alignment film described above requires a two-step process, that is, a baking process and an alignment process after the inorganic coating material is applied to a predetermined substrate. The alignment process requires a SiOx oblique deposition process. Therefore, there is a problem that it is difficult to improve productivity and cannot withstand practical use.

  In view of such a current situation, the present inventors have conducted research and development to make it possible to form an alignment film made of an inorganic material more easily, and have achieved the present invention.

  In the liquid crystal display device of the present invention, a substrate having an alignment film formed by applying an alignment treatment after coating a coating film composed of SiOx having a main chain of an inorganic siloxane skeleton and having an alkyl group in the side chain. It was decided to prepare.

Furthermore, the following points are also characteristic. That is,
(1) The alignment treatment is any one of rubbing treatment, optical alignment treatment, and beam treatment.
(2) A vertical alignment type liquid crystal having a refractive index of 0.10 to 0.20 and a negative dielectric anisotropy is filled between two substrates on which alignment films are formed, and the distance between the substrates is set to 3.0 μm or less. What you did.
(3) Drive by a one-field inversion driving method that inverts an applied voltage for each field.

  Further, in the method for manufacturing a liquid crystal display element of the present invention, in the method for manufacturing a liquid crystal display element in which liquid crystal is filled between two substrates, the alignment film is formed by aligning the coating film applied to each substrate. And the coating film is composed of SiOx having a main chain made of an inorganic siloxane skeleton and an alkyl group in the side chain.

  Further, the alignment process is characterized in that it is one of rubbing process, photo-alignment process, and beam process, and the liquid crystal is a vertical alignment type in which the refractive index is 0.10 to 0.20 and the dielectric anisotropy is negative. In addition, the distance between the substrates is 3.0 μm or less.

  In the present invention, the alignment film has an alkyl group in the side chain, but the main chain is composed of an inorganic siloxane skeleton, so that the light resistance of the alignment film is higher than when using an organic alignment film such as a conventional polyimide. The life of the liquid crystal display element can be extended.

  In addition, by having an alkyl group in the side chain, the application of a coating film to the substrate at normal pressure, and the usual rubbing treatment, photo-alignment treatment, or beam orientation treatment, etc. should be used. And can follow conventional manufacturing equipment.

  Furthermore, between the two substrates on which the alignment film is formed, a vertical alignment type liquid crystal having a refractive index of 0.10 to 0.20 and a negative dielectric anisotropy is filled, and the distance between the substrates is set to 3.0 μm or less. As a result, the reduction in transmittance can be suppressed.

  In addition, the influence of lateral electrolysis can be suppressed by driving by the one-field inversion driving method in which the applied voltage is inverted for each field.

  In the liquid crystal display element and the manufacturing method thereof according to the present invention, the main chain is composed of an inorganic siloxane skeleton, and the side chain has an alkyl group on the TFT substrate on which the alignment film is formed and the counter substrate facing the TFT substrate. An alignment film is formed by applying a coating film having a composition of SiOx having, and then performing an alignment treatment on the coating film.

  As described above, the alignment film has an alkyl group in the side chain, but the main chain is composed of an inorganic siloxane skeleton. Therefore, the alignment film is aligned as compared with the case of using an organic alignment film such as a conventional polyimide. The light resistance of the film can be improved by 2.6 times or more, and a lifetime of 7000 hours or more can be realized.

  Here, the definition of light resistance life is a value of 10% cumulative failure rate of conventional organic alignment films such as polyimide, using UV cut filter (half value λ = 430nm), brightness 2600ANSIlm, temperature 60 ℃. Since this is 3100 hours, this value was regarded as the lifetime of the organic alignment film. Of course, the light-resistant life varies depending on use conditions such as temperature, light quantity, incident light wavelength, and the like.

  By having an alkyl group in the side chain, the coating film can be applied to the substrate at normal pressure, and further, such as rubbing treatment, photo-alignment treatment, laser beam treatment or ion beam treatment, etc. Since the alignment process can be performed by any one of the beam alignment processes, it is possible to suppress an increase in manufacturing cost.

  As described above, the TFT substrate on which the alignment film is formed and the counter substrate are bonded to each other so that the liquid crystal injected and filled between the substrates has a refractive index of 0.10 to 0.20 and a negative dielectric anisotropy. The liquid crystal is a vertical alignment type liquid crystal, and the distance between the substrates is 3.0 μm or less.

  Therefore, a liquid crystal display element having high transmittance can be obtained without greatly reducing the transmittance.

  Furthermore, a polarizing plate having a polarization angle in a predetermined direction is mounted on each of the TFT substrate and the counter substrate to form a liquid crystal display element. The counter substrate facing the TFT substrate reverses the applied voltage for each field. It is driven by the driving method. Therefore, the influence of lateral electrolysis can be suppressed.

  In the following, more specific examples will be described.

  Here, as the alignment film, a 4% ethanol / butyl cellosolve solution of EXP-OA018 (manufactured by Nissan Chemical Co., Ltd.) is used as a coating film whose composition is composed of SiOx whose main chain is composed of an inorganic siloxane skeleton and has an alkyl group in the side chain. This coating film is applied to a required substrate by spin coating, dried on a hot plate at 80 ° C. for 5 minutes, and baked in a clean oven at 180 ° C. for 60 minutes. . The film thickness of the alignment film after firing is about 1000 angstroms.

  In particular, the skeleton of the main chain of the inorganic alignment film having an alkyl group in the side chain is based on a siloxane skeleton system as follows.

  In the alignment film, the liquid crystal molecules are vertically aligned under the influence of the long-chain alkyl group present in the side chain. However, this alone does not determine the direction in which the liquid crystal tilts when a voltage is applied. Therefore, alignment processing such as rubbing processing, photo-alignment processing, laser beam processing, or ion beam processing is required.

First embodiment: When rubbing treatment is used as orientation treatment
The above coating film is applied to a TFT substrate on which a 0.79-type XGA pixel pattern is formed to form an alignment film, and after the rubbing treatment, the alignment film is similarly formed and the opposite substrate on which the rubbing treatment is performed The substrates were stacked so that the orientation directions of the substrates were antiparallel, and liquid crystal having a refractive index ΔN = 0.15 (Merck, Δε = −6.0) and negative dielectric anisotropy was injected.

  Thereafter, the injection port was sealed, dust-proof glass was attached to the TFT substrate and the counter substrate, and a flexible substrate, an outer frame, and a parting plate were attached to complete the liquid crystal panel. The cell gap, which is the distance between the TFT substrate and the counter substrate, was 2.8 μm.

  Optical characteristics were examined with a projector-optical system evaluation apparatus for the produced liquid crystal display element. The driving method was evaluated by double speed field inversion driving. The counter substrate used at this time is a transparent substrate with a BLK matrix.

  The transmittance is 20.6% (21.1% in the case of a TN type 2.6 μm gap cell), which is a light transmittance that is not significantly different from that of the TN cell. Contrast was also obtained as 450: 1, which is not much different from 410: 1 of the TN cell.

Second embodiment: When ion beam processing is used as alignment processing
The above-mentioned coating film was applied to a TFT substrate on which a 0.79-type XGA pixel pattern was formed in a 300 mm wafer state to form an alignment film, and an ion beam was irradiated under the following conditions. The ion beam was irradiated in the form of a curtain, and the substrate was moved and oriented on the lower side. The film thickness after firing was 60 nm.

The conditions of the orientation experiment machine were a beam size of 200 mm × 60 mm, an ion species of N ₂ (nitrogen), an ion energy of ˜1500 eV, a transfer speed of 20 mm / sec, and an incident angle of 40 degrees from the normal direction.

  An alignment film was also formed on the counter substrate under the same conditions. In the assembly, the TFT substrate and the counter substrate were overlapped so that the orientation directions of the substrates were antiparallel. Since this was an experimental machine, the entire wafer was not irradiated with an ion beam. Therefore, a liquid crystal display element was assembled using the TFT substrate and the counter substrate at the portion irradiated with the ion beam. A liquid crystal with a negative dielectric anisotropy (Δε = −6.0) having a cell gap of 2.8 μm and a liquid crystal refractive index of ΔN = 0.15 was produced in the same manner as in Example 1.

  When the optical characteristics were measured in the same manner as in Example 1, a light transmittance of 20.7% and a contrast of 435: 1 were obtained.

Third Example: When Photo-Alignment Treatment is Used as the Alignment Treatment The alignment material is prepared by the method described above, and the UV light irradiation device is irradiated using ELSICON E2-UV-600-SS-AA Exposure Unit. .

The incident angle was 45 degrees, and polarized UV light (light intensity 300 mJ / cm ² ) with an appropriate ratio of P and S waves was irradiated for 3 minutes (light intensity 300 mJ / cm ² ) (FIGS. 2 and 3). When the pretilt angle was measured with the test cell under the same conditions, it was 3.5 degrees from the normal direction.

  In this way, alignment processing is performed on the TFT substrate side and the counter substrate side, a liquid crystal cell is assembled, and liquid crystal having a refractive index of ΔN = 0.16 and Δε = −5.3 is used. Got.

  The light transmittance was 20.6% and the contrast was 420: 1.

Claims (7)

  A liquid crystal display device comprising a substrate having an alignment film formed by applying an alignment treatment after coating a coating film composed of an inorganic siloxane skeleton and having an SiOx composition having an alkyl group on a side chain.   The liquid crystal display element according to claim 1, wherein the alignment treatment is one of rubbing treatment, optical alignment treatment, and beam treatment.   Between the two substrates on which the alignment film is formed, a vertical alignment type liquid crystal having a refractive index of 0.10 to 0.20 and a negative dielectric anisotropy is filled, and the distance between the substrates is set to 3.0 μm or less. The liquid crystal display element according to claim 1 or 2.   The liquid crystal display element according to claim 1, wherein the liquid crystal display element is driven by a one-field inversion driving method that inverts an applied voltage for each field. In a manufacturing method of a liquid crystal display element formed by filling a liquid crystal between two substrates,
A process of forming an alignment film by performing an alignment treatment on the coating film applied to each of the substrates;
A method of manufacturing a liquid crystal display element, wherein the coating film is composed of SiOx having a main chain made of an inorganic siloxane skeleton and having an alkyl group in a side chain.   The method for manufacturing a liquid crystal display element according to claim 4, wherein the alignment treatment is any one of rubbing treatment, optical alignment treatment, and beam treatment.   7. The liquid crystal according to claim 5, wherein the liquid crystal is a vertical alignment type having a refractive index of 0.10 to 0.20 and a negative dielectric anisotropy, and a distance between the substrates is 3.0 μm or less. A method for manufacturing a liquid crystal display element.