Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
  • G02F1/13378—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation
  • G02F1/133788—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation by light irradiation, e.g. linearly polarised light photo-polymerisation
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
  • G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
  • G02F1/1393—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells

Definitions

• the present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device with high display quality, which can provide a wide viewing angle and high-speed response, and can be widely applied to a TV, a monitor for personal computer and the like.
• Liquid crystal display panels in VA have been recently used for liquid crystal display devices such as a monitor for personal computers, and a TV, because of their wide viewing angle characteristic.
• VA Vertical Alignment
• liquid crystal display devices in MVA Multi-DomainVertical Alignment
• PVA Plasma Vertical Alignment
• both substrates are providedwith electrode slits to form a domain division.
• the response speed it is effective that alignment films provided on liquid crystal layer side surfaces of substrates are subjected to an alignment . treatment, whereby to provide liquid crystal molecules with pretilt angles previously. Also in VA mode, liquid crystal molecules are previouslymade slightly incline towardvertical alignment films, and thereby can easily incline when a voltage is applied to the liquid crystal layer . Therefore, the response speed can be made faster.
• a rubbing method, a SiOx oblique deposition method, and a photo-alignment method may be mentioned as methods of the alignment treatment for providing liquid crystal molecules with the pretilt angles .
• the domain division is performed to obtain a wide viewing angle in MVA mode and PVA mode.
• the domain division in MVA mode and PVA mode has room for improvement in that more alignment treatment steps are needed for alignment films.
• the rubbing method a method, in which a region to be rubbed and a region not to be rubbed are separated using a resist pattern to be subjected to a rubbing, has been proposed.
• the photo-alignment method a method, in which one or more times of exposures via a photomask is performed for the domain division, has been proposed. It is desirable that the number of times of such an alignment treatment is fewer in terms of simplification of production steps.
• VA mode in which the domain division is performed, proposed has beenVAmode (hereinafter, also referred to as VAECB (Vertical Alignment Electrically Controled Birefringence) mode) using vertical alignment films, in which alignment directions on each other' s substrates are antiparallel in any domain, as shown in Figs. HA, HB, 12-1 and 12-2.
• VAECB mode as shown in Fig.
• a direction of an absorption axis of a first polarizer 5 formed on a first substrate side and a direction of an absorption axis of a second polarizer 6 formed on a second substrate side are out of alignment with an alignment direction of a first alignment film IA and an alignment direction of second alignment direction 2A by 45 degrees.
• throughput in volume production decreases since the alignment treatment is performed in four directions, i.e. 45, 135, 225, and 315 degrees, as shown " in Fig. ' 12-2.
• Japanese Kokai Publication No. 2001-281569 discloses a technique, in which an alignment treatment is performed by a photo-alignment method to provide VAECB mode, but this technique needs a total of eight times of exposure processes for the alignment films ' .
• VAHAN Very Alignment Hybrid-aligned Nematic
• VAmode Vertical Alignment Twisted Nematic
• VAN Vertical Alignment Twisted Nematic
• vertical alignment films in which alignment treatment directions on each other' s substrates are perpendicular to each other to make liquid crystal molecules form a twist structure (for example, with reference to Japanese Kokai PublicationNo . Hei-ll-35248 ⁇ , Japanese Kokai Publication No.2002-277877, Japanese Kokai Publication No . Hei-11-133429, and Japanese Kokai PublicationNo. Hei-10-123576) .
• InVATNmode a direction of an absorption axis of a first polarizer and an alignment direction of a first alignment film are the same, and a direction of an absorption axis of a second polarizer and an alignment direction of a second alignment film are the same.
• the direction of the absorption axis of the first polarizer and the alignment direction of the second alignment film may be the same, and the direction of the absorption axis of the second polarizer and the alignment direction of the first alignment filmmay.be the same.
• a mode in which one pixel is divided into four domains in VATN mode, needs only four times of alignment treatments, which is half the number of times in VAECB mode.
• VATN mode is theoretically excellent in that fewer times ofprocesses canprovide a wide viewing angle andhigh-speed " response.
• a technique for producing a liquid crystal display device in VATN mode has not been established yet . There is room for improvement in display brightness characteristic and the like.
• the present invention has been made in view of the above-mentioned state of the art.
• the present invention has an object to provide a liquid crystal display device capable of providing an improved display brightness characteristic in VATN mode using vertical alignment films, in which alignment treatment directions on each other's substrates are perpendicular to each other.
• the present inventors have tried to simplify alignment treatment processes for an alignment film. They have made various investigations about liquid crystal display devices capable of providing a wide viewing angle and high-speed response . They have noted VATN mode using vertical alignment films, in which alignment directions on each other's substrates are perpendicular to each other. However, the results of the investigation showed that it is difficult to obtain a stable transmittance and provide sufficient display brightness characteristic in VATN mode . They have further studied on VATN mode, and foundthat inVATNmode, a transmittance largely depends on variation in pretilt angle of liquid crystal molecules, such as a difference in pretilt angles between the liquid crystal molecules near an alignment film (first alignment film) provided on one substrate and the liquid crystal molecules near an alignment film (second alignment film) provided on the other substrate.
• aphoto-alignment film made of a material having a photosensitive group makes it possible to control such a difference in pretilt angles between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film to less than 1.0 degree, whereby to provide a stable transmittance .
• the present invention provides a liquid crystal display device comprising a first substrate, a second substrate, a liquid crystal layer provided between the substrates, a first alignment film provided on the liquid crystal layer side surface of the first substrate, and a second alignment film provided on the liquid crystal layer side surface of the second substrate, wherein the liquid crystal layer includes liquid crystal molecules with negative dielectric anisotropy, the first alignment film and the second alignment film align the liquid crystal molecules substantially vertically to the alignment film surfaces and align the liquid crystal molecules near the first alignment film and the second alignment film such that alignment directions of the liquid crystal molecules near the first and second alignment .films are perpendicular to each other, and the first alignment film and the second alignment film are photo-alignment films made of a material having a photosensitive group.
• the present invention also provides a liquid crystal displaydevice comprising, a first substrate, a second substrate, a liquid crystal layer provided between the substrates, a first alignment film provided on the liquid crystal layer side surface of the first substrate, and a second alignment film provided on the liquid crystal layer side surface of the second substrate, wherein the liquid crystal layer includes liquid crystal molecules with negative dielectric anisotropy, the first alignment film and the second alignment film align the liquid crystal molecules substantially vertically to the alignment film surfaces and align the liquid crystal molecules near the first alignment film and the second alignment film such that alignment directions of the liquid crystal molecules near the first and second alignment films are perpendicular to each other, and a difference in pretilt angles between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film is less than 1.0 degree .
• Figs. IA and IB are conceptual views each showing a drive principle of a liquid crystal display device in VATN mode in Embodiment 1.
• Fig. IA shows OFF-state
• Fig. IB shows ON-state.
• Figs. 2-1A and 2-1B are conceptual views each showing positional relationships of alignment directions of alignment films and absorption axes of polarizers in one domain of the liquidcrystal displaydevice inVATNmode inEmbodiment 1.
• Figs . 2-1A and 2-1B each show one example of the positional relationships.
• Fig. 2-2 is a conceptual view showing a relationship of four domains and alignment directions of alignment films in one pixel of the liquid crystal display device in VATN mode in Embodiment 1.
• Fig. 3 is a conceptual view showing a pretilt angle of a liquid crystal molecule.
• Fig. 4 is a graph showing each relationship of a pretilt angle and a contrast ratio in liquid crystal display devices in VATN mode and VAECB mode.
• Fig.5A shows a change in voltage-transmittance curve when a pretilt angle is changed in a liquid crystal display device in VATN mode .
• Fig. 5B shows a change in voltage-transmittance curve when a pretilt angle is changed in a liquid crystal display device in VAECB mode.
• Fig. 6 is a graph showing each change in transmittance at 6.2 V when a pretilt angle of liquid crystal molecules near the second alignment film is changed in liquid crystal display devices in VATN mode and in VAECB mode.
• Figs. 7A and 7B are graphs each showing tilt angles and azimuthal angles of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is
• Fig. 7A shows OFF-state
• Fig. 7B shows ON-state.
• Figs .8Aand 8B are graphs showing tilt angles and azimuthal angles of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 89.0 degrees and a pretilt angle of the liquid crystal molecules near a secondalignment filmis 88.5 degrees in a liquidcrystal display device in VATN mode.
• Fig. 8A shows OFF-state
• Fig. 8B shows ON-state.
• Figs .9Aand 9B are graphs showing tilt angles and azimuthal angles of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 89.5 degrees and a pretilt angle of the liquid crystal molecules near a second alignment filmis 88.5 degrees in a liquid crystal display device in VATN mode.
• Fig.9A shows OFF-state
• Fig. 9B shows ON-state.
• Figs. 1OA and 1OB are graphs showing tilt angles and azimuthal angles of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 89.5 degrees and a pretilt angle of the liquid crystal molecules near a second alignment film is 88.5 degrees in a liquid crystal display device in VAECB mode.
• Fig. 1OA shows OFF-state
• Fig. 1OB shows ON-state.
• Figs . HA and HB are conceptual views each showing a drive principle of a liquidcrystal display device inVAECB mode.
• Fig. HA shows OFF-state
• Fig. HB shows ON-state.
• Fig. 12-1 is a conceptual view showing positional . relationships of alignment directions of alignment films and absorption axes of polarizers in one domain of a liquid crystal display device in VAECB mode.
• Fig. 12-2 is a conceptual view showing a relationship of four domains and alignment directions of alignment films in one pixel of a liquid crystal display device in VAECB mode.
• first alignment film IA alignment direction of first alignment film
• pretilt angle 5 direction of an absorption axis of first polarizer
• the liquid crystal display device comprises, as a basic configuration of liquid crystal displaydevice, a first substrate and a second substrate, a liquid crystal layer provided between the first and second substrates, a first alignment film provide on the liquid crystal layer side surface of the first substrate, and a second alignment film provided on the liquid crystal layer side of the second substrate .
• the configuration of the liquid crystal display device according to the present invention is not especially limited as long as the above-mentioned components are essentially comprised.
• the liquid crystal display device may or may not comprise other components .
• the liquid crystal layer includes liquid crystal molecules with negative dielectric anisotropy, and the first alignment film and the second alignment film align the liquid crystal molecules substantiallyvertically to the alignment film surfaces andalign the liquid crystal molecules near the first alignment film and the second alignment film such that alignment directions of the liquid, crystal molecules near the first and second alignment films are perpendicular to each other .
• Use of the liquid crystal layer and the alignment film makes it possible to provide a liquid crystal display device in VATN mode in which the liquid crystal molecules align substantially vertically to the substrate surfaces and form a twist structure between the substrates .
• the liquid crystal display device has at least one of the following configurations (1) and (2) : (1) a configuration, in which the first alignment film and the second alignment film (hereinafter, also referred to as “alignment filmof thepresent invention") are photo-alignment films made of a material having a photosensitive group (hereinafter, also referred to as "photosensitive material”) ; and (2) a configuration, in which a difference in pretilt angles between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film is less than 1.0 degree.
• the "photo-alignment film” means a film made of a material, in which an alignment regulating force changes by light irradiation .
• the material having a photosensitive group (photosensitive material) in the above configuration (1) includes no materials generating photodecomposition (photodecomposition type materials) .
• the pretilt angle of the liquid crystal molecules is controlled with high accuracy near the first and second alignment films.
• Preferable configurations in the above-mentioned configuration (1) are as follows : (1-1) a configuration, in which the photo-alignment films provide the liquid crystal molecules near the first alignment film and the second alignment films with substantiallyuniformpretilt angles; (1-2) a configuration, in which the pretilt angles of the liquid crystal molecules near the first alignment film and the second alignment film are 89 degrees or less; (1-3) a configuration, in which the first alignment film and/or the second alignment film are/is photo-alignment films/a photo-alignment filmmade of a material having at least one photosensitive group selected from the group consisting of a 4-chalcone group (the following formula (I)), a 4' -chalcone group (the following formula (2)), a coumarin group (the following formula (3) ) , and a cinnamoyl group (the following formula (4) ) ; and (1-4) a configuration, in which each of the first alignment film and the second alignment film has at least one structure selected from the group consisting of
• the photosensitive group in the following formulae (1) to (4) may have a structure in which a substituent group is bonded to the benzene ring.
• a bond-structure, a photoisomerization structure, and a photo-realignment structure of the photosensitive group means that a bond-structure of the photosensitive group, a photoisomerization structure of the photosensitive group, and a photo-realignment structure of the photosensitive group.
• the variation in pretilt angle can be effectively suppressed, and a stable transmittance can be easily provided in liquid crystal display devices in VATN mode.
• the term "substantially uniform" means that the pretilt angles need not to be exactly uniform but need to be uniform enough for achievement of effects of the present invention. More specifically, in the above configuration (1-1), a difference in pretilt angles between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film is preferably less than 1.0 degree, and more preferably 0.5 degrees or less.
• the above configuration (1-2) can provide liquid crystal display devices in VATN mode having a high transmittance equivalent of liquid crystal display devices in VAECB mode.
• the photosensitive groups represented by the formulae (1) to (4) generate a crosslinking. reaction (including dimerization reaction) , an isomer!zation reaction, a photo-realignment, and the like.
• a crosslinking. reaction including dimerization reaction
• an isomer!zation reaction an isomer!zation reaction
• a photo-realignment and the like.
• Such a configuration can effectively suppress the variation in pretilt angle, and therefore can provide liquid crystal display devices inVATNmode having a stable transmittance.
• a dimerization reaction is generated by light irradiation as shown in the following formulae (5) and (6), and also a trans-cis isomerization reaction is generated, as shown in the following formula (7) .
• the above-mentioned material having a photosensitive group is a material generating a photobonding reaction (photobonding type material) .
• the alignment film of the present invention is a photobonding type alignment film.
• the above configuration (1-4) also can effectively suppress the variation in pretilt angle . Therefore, such a configuration is a preferable configuration for providing liquid crystal display device in VATN mode having a stable transmittance .
• Thebond-structure of the photosensitive group in the above configuration (1-4) means a structure, in which photosensitive functional groups contained in constituent molecules of the photosensitive material are bonded to each other by light irradiation. It is preferable that the bond-structure of the photosensitive group in the above configuration (1-4) is formed by a crosslinking reaction. In this case, the bond-structure can be formed, for example, by irradiation of light with a wavelength of 250 to 400 run.
• the above-mentioned crosslinking reaction includes a dimerization reaction and means that a chemical bond is formed between some specific atoms in a linear polymer molecule .
• the above-mentionedphotosensitivematerial generally has a molecular structure, in which a plurality of side chains is bonded to a linear main chain, and the side chain contains a photosensitive group (photoreaction group) . Therefore, in the above-mentioned photosensitive material, a crosslinking reaction such as a dimerization reaction of the photosensitive group is generated by light irradiation between two side chains to form a crosslinking structure. Therefore, the alignment film of the present invention has a bond-structure of the photosensitive group.
• the photoisomerization structure of the photosensitive group in the above configuration (1-4) means a structure, in which a photosensitive functional group contained in the constituent molecules of the photosensitive material has been isomerizedby light irradiation. Therefore, the alignment film of the present invention having such a photoisomerization structure of the photosensitive group has a structure, for example, in which the photosensitive group of cis isomerism (or trans isomerism) contained in the photosensitive material has changed to that of trans isomerism (or cis isomerism) through excited state by light irradiation.
• the photo-realignment structure of the photosensitive group in the above configuration (1-4) means a structure, in which a photosensitive functional group contained in the constituent molecules of the photosensitive material has been photo-realigned.
• the "photo-realignment” means that a photosensitive functional group contained in the constituent molecules of the photosensitive material changes its direction by light irradiation without being isomerized. Therefore, the alignment film of the present invention having such a
• photo-alignment structure of the photosensitive group has a structure, for example, in which the photosensitive group of cis isomerism (or trans isomerism) contained in the photosensitive material has changed its direction while remaining its isomerism through excited state by light irradiation.
• the alignment film of the present invention may include a photosensitive group contained in the photosensitive material as it is, as in the above cases where the alignment film of the present invention has the photoisomerization structure or the photo-realignment structure in the above configuration (1-4) .
• the photobonding type alignment film generally exhibits an alignment regulating force by light irradiation in a state where the bond-structure, the photoisomerization structure, and the photo-realignment structure of the photosensitive group are mixed.
• a difference in pretilt angles between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film is 0.5 degrees or less in the above-mentioned configuration (2) . In this case, the variation in pretilt angle can be effectively suppressed.
• configuration (2) preferred is a configuration (2-1) , in which the pretilt angles of the liquid crystal molecules near the first alignment film and the second alignment film are 89 degrees or less.
• Such a configuration can provide a liquid crystal display device, even in VATN mode, having a high transmittance equivalent of a liquid crystal display device in VAECB mode.
• configuration (2) preferred is a configuration (2-2), in which the first alignment film and/or the second alignment film are/is photo-alignment films/a photo-alignment film made of a material having at least one photosensitive group selected from the group consisting of a 4-chalcone group (the above formula (I)), a
• the photosensitive group in the above formulae (1) to (4) may have a structure in which a substituent group is bonded to the benzene ring. Such a configuration can effectively suppress the variation in pretilt angle, similar to the above configuration (1-3) . Therefore, liquidcrystal display devices in VATN mode having a stable transmittance can be produced.
• the first alignment film and/or the second alignment film are/is photo-alignment films/a photo-alignment film made of a material having the cinnamate group, from the same viewpoint as in the above configuration of (1-3) .
• the first alignment film and the second alignment film each has two or more regions in one pixel, and among the two or more regions, an alignment direction is different.
• a domain division allows for a wide viewing angle.
• VATN mode for example, two regions having alignment directions different to each other by substantially 180 degrees are formed on both the first alignment film and the second alignment film. And the two alignment films are placed opposite such that the alignment direction of the first alignment film and the alignment direction of the second alignment film are perpendicular to each other. Thereby, four domains are formed in one pixel because each region of the first alignment film are divided and alignedby each region of the second alignment film.
• the alignment treatment processes inVATNmode can be reduced as compared to VAECB mode, because VAECB mode needs a total of eight times of alignment treatment processes, inwhich four times of alignment treatment processes are provided
• each alignment film has two or more regions in one pixel, and among the two or more regions, an alignment direction is different. Thereby, the one pixel can be divided' into four or more domains, whereby to provide a sufficient viewing angle.
• the liquid crystal display device of the present invention can provide a stable transmittance and thereby improves a display brightness characteristic in VATN mode using vertical alignment films, in which alignment directions on each other' s substrates are perpendicular to each other.
• Figs. IA and IB are conceptual views each showing a drive principle of a liquid crystal display device in VATN mode in Embodiment 1.
• Fig. IA shows OFF-state
• Fig. IB shows ON-state.
• the first alignment film and the second alignment film align the liquidcrystal molecules substantiallyvertically to the alignment film surfaces (the substrate surfaces) andalign the liquid crystal molecules near the first alignment film and the second alignment film such that alignment directions of the liquid crystal molecules near the first and second alignment films are perpendicular to each other, at OFF-state when the voltage applied between the substrates interposing the liquid crystal layer is less than a threshold voltage.
• the "alignment direction of the liquid crystal molecules” means a direction shownby projecting a tilt direction of the liquid crystal molecule near the first or second alignment film on to the substrate surface.
• alignment directions of the liquid crystal molecules near the first and second alignment films are perpendicular to each other means that the alignment direction of the liquid crystal molecules near the first alignment film and the alignment direction of the liquid crystal molecules near the second alignment film do not necessarily need to be completely perpendicular to each other as long as the liquid crystal molecules can be aligned such that the alignment directions are substantiallyperpendicular to each other to provide liquid crystal display in VATN mode.
• the alignment direction of the first alignment film and the alignment direction of the second alignment film preferably cross at 85 to 95 degrees . As shown in Fig.
• the liquid crystal molecules with negative dielectric anisotropy align parallel to the substrate surfaces depending on the applied voltage , and show birefringence to light transmitted through the liquid crystal display panel, at ON-state when the voltage applied between the substrates interposing the liquid crystal layer is more than a threshold voltage.
• a production method of the liquid crystal display device in VATN mode in Embodiment 1 is hereinafter described.
• Embodiment 1 a pair of a first substrate and a second substrate each having no alignment film were first prepared by a usual method.
• a thin film transistor array substrate was prepared as the first substrate that was one substrate.
• the thin film transistor array substrate was prepared: by forming scanning signal lines and data signal lines so as to intersect with each other on grid with an insulating film therebetween on a glass substrate; and by forming a thin film transistor and a pixel electrode at eachof the intersections, the scanning signal line , the data signal line, the thin film transistor and the pixel electrode being provided by the following (1) to (6) steps of: forming a stacked body of thin films; and then patterning the
• PCVD plasma-enhanced Chemical vapor deposition
• an exposure step using an exposure method such as a lens projection (stepper) method, a mirror projection method, and a proximity method
• a color filter substrate was prepared as the second substrate that was the other substrate.
• the color filter substrate was preparedby successively forming (1) ablackmatrix, (2) a colored pattern of RGB, (3) a protective film, and (4) a transparent electrode film on a glass substrate.
• an alignment film material photosensitive material
• a solution containing an alignment film material was applied to the first and second substrates by the spin cast method, and then the substrates were calcined at 180 degrees C for 60 minutes to form alignment films .
• Amaterial containing 4-chalcone group was used as the alignment film material in Embodiment 1.
• pretilt angles of the liquid crystal molecules near the first alignment film and the second alignment film were each set at 88.5 degrees by an alignment treatmentby light irradiation along alignment directions shown in Fig. 2-1.
• the alignment treatment was performed by emitting p-polarized light with a wavelength of 365 nm to alignment films at an incident angle of 40 degrees, at 3 mW/cm 2 for 400 seconds .
• Constituent molecules of the alignment film have a photofunctional group (photosensitive group) at a side chain of a polymer chain. And "the photofunctional group forms a dimer by a dimerization reaction caused by the above-mentioned alignment treatment, whereby to form a crosslinking structure (cross-linking bond structure) .
• Part of the constituent molecules of the alignment film generates an cis-trans isomerization through an isomerization reaction caused by the alignment treatment, and another part of the constituent molecules generates a photo-realignment by the alignment treatment.
• each pixel region on the first substrate was divided into two regions for alignment treatment and the two regions were each irradiated with light in opposite directions to each other.
• eachpixel region on the second substrate was similarly divided into two regions for alignment treatment and the two regions were each irradiated with light in opposite directions to each other.
• a liquid crystal display panel in VATN mode was produced by an alignment treatment by light irradiation in the same manner as in Embodiment 1, except that a photodecomposition type alignment filmmaterial was used as-the alignment filmmaterial, and p-polarized light with a wavelength of 254 nm was emitted to alignment films at 2 mW/cru 2 for 500 seconds to generate a photodecomposition reaction in constituent molecules of the alignment films.
• a plurality of liquid crystal display panels prepared by the method in the above-mentioned Embodiment 1 or Comparative Embodiment 1 was measured for pretilt angle.
• the pretilt angle was measured with commercially available measurement device for tilt angle (trade name: OPTIPRO, product of Shintex Japan Corp. ) .
• the measurement results show that the liquid crystal display panels having the photobonding (dimerization) alignment film, which were produced by the method in Embodiment 1 , have a pretilt angle of 88.5 ⁇ 0.5 degrees.
• the measurement results shows that the liquid crystal display panels having the photodecomposition type alignment film, which were produced by the method in Comparative Embodiment 1, have a pretilt angle of 88.5+1.0 degrees.
• the above-mentioned measurement device provides an averaged value of the pretilt angle near the first alignment film and the pretilt angle near the second alignment film.
• a variation in the averaged values of the pretilt angles measured in the plurality of liquid crystal display panels shows that a difference in pretilt angle between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film was +0.5 degrees if the photobonding (dimerization) alignment film was used (in Embodiment 1) .
• a difference in pretilt angle between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film was ⁇ 1.0 degree if the photodecomposition type alignment film was used (in Comparative Embodiment 1) .
• the "pretilt angle” means, as shown in Fig. 3, an angle formed by the alignment film surface and a longitudinal direction of the liquid crystal molecule near the alignment film when a voltage less than a threshold voltage is applied to the liquid crystal layer (at OFF-state) .
• an angle formed by the alignment film surface and the longitudinal direction of the liquid crystal molecule near the alignment film, regardless of OFF state or ON state, is called tilt angle or polar angle.
• the material, which changes the conformation by the bonding reaction, and the like, of the photosensitive group caused by light irradiation was used to control the pretilt angle of the liquid crystal molecules, the variation in pretilt angle was ⁇ 0.5 degrees, which was smaller than the variation in pretilt angle in Comparative Embodiment 1. Therefore, a stable pretilt angle can be provided. This is because the bonding reaction of the photosensitive group has a saturation characteristic to the amount of light irradiation.
• the variation in pretilt angle was ⁇ 1.0 degree, which was larger than the variation in pretilt angle in Embodiment 1, because the material generating the photodecomposition reaction caused by the light irradiation was used to control the pretilt angle of the liquid crystal molecules.
• the pretilt tends to inclinemore andmore as the amount of light irradiationbecomes larger, that is, the photodecomposition reaction exhibits no saturation characteristic, and therefore the variation in amount of light irradiation is directly linked to the variation in pretilt angle.
• Embodiment 1 show that the control of the variation in pretilt angle is important for display uniformity in VATN mode, and that as the pretilt angle on the first substrate and the pretilt angle on the second substrate becomes asymmetric, the transmittance decrease more and more. And it turns out that use of the photobonding (dimerization) alignment film is effective for the suppression of the variation in pretilt angle.
• an alignment film formed on a substrate in Im or more on a side is usually subjected to an alignment treatment for increase in size of a liquid crystal display TV and improvement in production efficiency. Accordingly, unevenness in irradiance of exposure on the substrate surface is difficult to prevent completely.
• a liquid crystal display device in VATN mode was prepared.
• the liquid crystal display devices had an alignment filmprepared by changing the strength and time of the light irradiation in the alignment treatment by light irradiation in Embodiment 1 to set pretilt angles of liquid crystal molecules near the first alignment film and the second alignment film at 85 to 90 degrees .
• the pretilt angle can be controlled by adjusting the material for the alignment film, the light irradiation angle, and the like. If the material for the alignment film is adjusted, the pretilt angle can be controlled by adjusting a component and the number of a side chain, a polar group and the like. If the light irradiation angle is adjusted, the pretilt angle can be larger by increasing an irradiation angle.
• Fig. 4 is a graph showing each relationship of a pretilt angle and a contrast ratio in liquid crystal display devices in VATN mode and VAECB mode. And Fig. 4 shows the case where the pretilt angles of the liquid crystal molecules near the first alignment film and the second alignment film are the same.
• VATN mode has an advantage over VAECB mode in terms of high contrast ratio. That is, VATN mode shows a smaller decrease in contrast ratio than that in VAECB mode when the pretilt angle is decreased, and the decrease in contrast ratio can be suppressed to 10% or less to the maximum contrast ratio in VATN mode.
• VATN mode has an advantage over VAECB mode in terms of improvement of response speed, because the decrease in contrast ratio is small if the pretilt angle is decreased.
• Fig.5A shows a change in voltage-transmittance curve when a pretilt angle is changed in a liquid crystal display device in VATN mode.
• Fig. 5B shows a change in voltage-transmittance curve when a pretilt angle is changed in a liquid crystal display device in VAECB mode.
• Figs. 5A and 5B each show the case where the pretilt angle of the liquid crystal molecules near the first alignment film was fixed at 88.5 degrees.
• Fig. 6 is
• ⁇ a graph showing each change in transmittance at 6.2 V when a pretilt angle of liquid crystal molecules near the second alignment film is changed in liquid crystal display devices in VATN mode and in VAECB mode.
• Fig. 6 shows the case where the pretilt angle of the liquid crystal molecules near the first alignment film was fixed at 88.5 degrees.
• VATNmode shows excellent risingproperty of transmittance
• VATN mode shows a large decrease in transmittance as compared with VAECB mode, as the difference in pretilt angle between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film increases. Therefore, it is shown that it is extremely important to control the pretilt angle for improvement in display properties in VATN mode.
• Fig. 6 shows that VATN mode stably provides high transmittance when the pretilt angle of the liquid crystal molecules near the second alignment film is 87.5 to 89.0 degrees.
• Figs .7A to 1OB each show tilt angles and azimuthal angles of the liquid crystal molecules at OFF state (voltage applied to the liquid crystal layer: 1.5 V) and at ON state (voltage applied to the liquid crystal layer : 6.2 V) in the above-mentioned liquid crystal display devices in VATN mode and VAECB mode.
• Figs. 7A and 7B are graphs each showing tilt angles and azimuthal angles of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 88.5 degrees and the pretilt angle of the liquidcrystal molecules near a second alignment film is 88.5 degrees in a liquid crystal display device in VATN mode.
• Fig. 7A shows OFF-state
• Fig. 7B shows ON-state. As shown in Fig.
• the liquid crystal molecule has a constant tilt angle (tilt angle of the liquid crystal molecule to "the substrate surface) of 88.5 degrees, "and an azimuthal angle of the liquid crystal molecule changes at a constant rate from -45 degrees to +45 degrees, from the first substrate toward the second substrate, at OFF state when a voltage applied between the substrates interposing the liquid crystal layer is less than a threshold voltage.
• the liquid crystal molecules near the first and second alignment films have tilt angles substantially vertical to the alignment films due to the alignment films, but the liquid crystal molecules at the center far from the alignment films have tilt angles substantially parallel to the alignment films due to the voltage applied to the liquid crystal layer.
• the azimuthal angles of the liquid crystalmolecules near the first and second alignment films largely change at almost the same rate.
• the azimuthal angle of the liquid crystal molecules at the center far from the alignment films shows a small change at a constant rate from the first substrate toward the second substrate.
• Figs.8Aand 8B are graphs showing tilt angles and azimuthal angles of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 89.0 degrees and a pretilt angle of the liquid crystal molecules near a second alignment film is 88.5 degrees in a liquid crystal display device in VATN mode/ Fig. 8A shows OFF-state, and Fig. 8B shows ON-state.
• Figs. 9A and 9B are graphs showing alignment directions of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 89.5 degrees and a pretilt angle of the liquid crystal molecules near a second alignment filmis 88.5 degrees in a liquid crystal display device in VATN mode .
• Fig. 8A shows OFF-state
• Fig. 8B shows ON-state.
• Figs. 9A and 9B are graphs showing alignment directions of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 89.5 degrees and a pretil
• Fig. 9A shows OFF-state
• Fig. 9B shows ON-state
• a tilt angle of the liquid crystal molecules changes from the first substrate toward the second substrate at an almost constant rate from 89.0 degrees (Fig. 8A) or 89.5 degrees (Fig.9A) to 88.5 degrees at OFF state
• an azimuthal angle of the liquid crystal molecules changes from -45 degrees to +45 degrees, from the first substrate toward the second substrate, slightly largely on the first substrate side.
• Figs. 8A a tilt angle of the liquid crystal molecules changes from the first substrate toward the second substrate at an almost constant rate from 89.0 degrees (Fig. 8A) or 89.5 degrees (Fig.9A) to 88.5 degrees at OFF state
• an azimuthal angle of the liquid crystal molecules changes from -45 degrees to +45 degrees, from the first substrate toward the second substrate, slightly largely on the first substrate side.
• the liquid crystal molecules near the first and second alignment films have tilt angles substantially vertical to -the alignment films due to the alignment films, but the liquid crystal molecules at the center far from the alignment films have tilt angles substantially parallel to the alignment films due to the voltage applied to the liquid crystal layer at ON state.
• the azimuthal angle of the liquid crystal molecules near the first alignment film having a larger tilt angle changes at a rate larger than that near the second alignment film.
• the changes of the azimuthal angle (twist of the liquid crystal molecules) on the first substrate side and that on the second substrate side are not symmetric when the pretilt angles near the first and second alignment films are different. Therefore, the transmittance decreases.
• Figs. 1OA and 1OB are graphs showing tilt angles and azimuthal angles of liquid crystal molecules when a pretilt angle of the liquid crystal molecules near a first alignment film is 89.5 degrees and a pretilt angle of the liquid crystal molecules near a second alignment film is 88.5 degrees in a liquid crystal display device in VAECB mode.
• Fig. 1OA shows OFF-state
• Fig. 1OB shows ON-state.
• the tilt angle of the liquid crystal molecule changes, from the first substrate toward the second substrate, at an almost constant rate from
• the liquid crystal molecules near the first and second alignment films have tilt angles substantially
• the liquid crystal molecules at the center far from the alignment films have tilt angles substantially parallel to the alignment films due to the voltage applied to the liquid crystal layer at ON state.
• the liquid crystal molecule has a constant azimuthal angle of 0 degree at ON and OFF state . Therefore, in VAECB mode, the difference in pretilt angle between the liquid crystal molecules near the first alignment film and the liquid crystal molecules near the second alignment film basically does not change the behavior of the liquid crystal molecules . Therefore, the transmittance hardly changes as shown in Fig. 6.
• the great characteristic of the present invention is that uniformization of the pretilt angle makes it possible to provide a stable transmittance and an excellent display brightness characteristic in VATN mode.

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