Liquid crystal display device

Abstract

The present invention provides a liquid crystal display device that includes a horizontal alignment film, stabilizes liquid crystal alignment by the PSA technique, can suppress the increase in power consumption, reduction in contrast, and image sticking in display, and has long-term reliability. The present invention is a liquid crystal display device including a pair of substrates, a liquid crystal layer interposed between the pair of substrates, a horizontal alignment film formed on at least one of the pair of substrates, and a polymer layer which is formed on the horizontal alignment film and controls the alignment of adjacent liquid crystal molecules, wherein the polymer layer is formed by the polymerization of at least one or more kinds of monomers added into the liquid crystal layer, and at least one of the one or more kinds of monomers is polymerized by itself functioning as a polymerization initiator by being irradiated with light.

Claims

1. A liquid crystal display comprising: a pair of substrates; a liquid crystal layer interposed between the pair of substrates; a horizontal alignment film formed on at least one of the pair of substrates; and a polymer layer formed on the horizontal alignment film, wherein the polymer layer is formed by the polymerization of at least two or more kinds of monomers added into the liquid crystal layer, at least one monomer of said two or more kinds of monomers have a structure that generates a radical when irradiated with visible light, said two or more kinds of monomers include the following first and second monomers first monomer ##STR00012## second monomer ##STR00013## the horizontal alignment film is an alignment film to which an alignment-controlling function is imparted by photo-alignment treatment, and an alignment film material that forms said horizontal alignment film includes a photoreactive functional group, and the photoreactive functional group is at least one kind of functional group selected from a group consisting of a cinnamoyl group, a diarylethene group, an anthrylene group, a chalcone group, a coumarin group, a cinnamate group, an azobenzene group, and a stilbene group, wherein the polymer layer, in addition to structures formed by said first and second monomers, has a structure represented by the following chemical formula (1) in a repeating unit, ##STR00014## in chemical formula (1), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, Q represents a monovalent organic group, and R represents a divalent group that includes a structure selected from the following chemical formula group (2), ##STR00015## in chemical formula group (2), a portion or all of hydrogen atoms may be substituted with a halogen atom, in addition, the respective ring structures may be a hetero ring in which a carbon atom is substituted with another atom.

2. A liquid crystal display comprising: a pair of substrates; a liquid crystal layer interposed between the pair of substrates; a horizontal alignment film formed on at least one of the pair of substrates; and a polymer layer formed on the horizontal alignment film, wherein the polymer layer is formed by the polymerization of at least two or more kinds of monomers added into the liquid crystal layer, at least one monomer of said two or more kinds of monomers have a structure that generates a radical when irradiated with visible light, said two or more kinds of monomers include the following first and second monomers first monomer ##STR00016## second monomer ##STR00017## the horizontal alignment film is an alignment film to which an alignment-controlling function is imparted by photo-alignment treatment, and an alignment film material that forms said horizontal alignment film includes a photoreactive functional group, and the photoreactive functional group is at least one kind of functional group selected from a group consisting of a cinnamoyl group, a diarylethene group, an anthrylene group, a chalcone group, a coumarin group, a cinnamate group, an azobenzene group, and a stilbene group, wherein the polymer layer, in addition to structures formed by said first and second monomers, includes a structure represented by the following chemical formulas (3), (4), (5), (6) or (7) in a repeating unit, ##STR00018## ##STR00019## in chemical formulae (3) and (4), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, and Q represents a monovalent organic group, ##STR00020## in chemical formula (5), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, R represents a divalent group including a benzene ring structure that is bonded at least to Y, and Q represents a monovalent organic group that includes a benzene ring structure that is bonded to the R moiety, ##STR00021## in chemical formula (6), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, R represents a divalent group including a benzene ring structure that is bonded at least to Y, and Q represents a monovalent organic group that includes a polymer chain, ##STR00022## in chemical formula (7) each of X and X′ independently represents —H or —CH.sub.3, each of Y and Y′ independently represents —O—, —COO—, —CONH—, or a direct bond, and R represents a divalent group including a benzene ring structure that is bonded at least to Y, and wherein said display employs an in-plane switching mode or fringe field switching mode as a display mode.

3. The liquid crystal display device according to claim 2, wherein said horizontal alignment film comprises polyimide, polyamic acid, polymaleimide, or polysiloxane.

4. The liquid crystal display device according to claim 2, wherein the polymer layer, in addition to structures formed by said first and second monomers, includes a structure represented by chemical formula (3) or chemical formula (4) in a repeating unit.

5. The liquid crystal display device according to claim 2, wherein the polymer layer, in addition to structures formed by said first and second monomers, includes a structure represented by chemical formula (5) in a repeating unit.

6. The liquid crystal display device according to claim 2, wherein the polymer layer, in addition to structures formed by said first and second monomers, includes a structure represented by chemical formula (6) in a repeating unit.

7. The liquid crystal display device according to claim 2, wherein the polymer layer, in addition to structures formed by said first and second monomers, includes a structure represented by chemical formula (7) in a repeating unit.

8. A liquid crystal display device comprising: a pair of substrates; a liquid crystal layer interposed between the pair of substrates; a horizontal alignment film formed on at least one of the pair of substrates; and a polymer layer formed on the horizontal alignment film, wherein the polymer layer is formed by the polymerization of at least two or more kinds of monomers added into the liquid crystal layer, at least one monomer of said two or more kinds of monomers have a structure that generates a radical when irradiated with visible light, said two or more kinds of monomers include the following first and second monomers first monomer ##STR00023## second monomer ##STR00024## the horizontal alignment film is an alignment film to which an alignment-controlling function is imparted by photo-alignment treatment, and an alignment film material that forms the horizontal alignment film includes a cyclobutane skeleton in a repeating unit, wherein the polymer layer, in addition to structures formed by said first and second monomers, has a structure represented by the following chemical formulas (8), (10), (11), (12), (13), or (14) in a repeating unit, ##STR00025## in chemical formula (8), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, Q represents a monovalent organic group, and R represents a divalent group including a structure selected from the following chemical formula group (9), ##STR00026## in chemical formula group (9), a portion or all of hydrogen atoms may be substituted with a halogen atom, in addition, the respective ring structures may be a hetero ring in which a carbon atom is substituted with another atom, ##STR00027## in chemical formulae (10) and (11), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, and Q represents a monovalent organic group, ##STR00028## in chemical formula (12), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, R represents a divalent group including a benzene ring structure that is bonded at least to Y, and Q represents a monovalent organic group that includes a benzene ring structure that is bonded to the R moiety, ##STR00029## in chemical formula (13), X represents —H or —CH.sub.3, Y represents —O—, —COO—, —CONH—, or a direct bond, R represents a divalent group including a benzene ring structure that is bonded at least to Y, and Q represents a monovalent organic group that includes a polymer chain, ##STR00030## in chemical formula group (14) each of X and X′ independently represents —H or —CH.sub.3, each of Y and Y′ independently represents —O—, —COO—, —CONH—, or a direct bond, and R represents a divalent group including a benzene ring structure that is bonded at least to Y, and wherein said display employs an in-plane switching mode or fringe field switching mode as a display mode.

9. The liquid crystal display device according to claim 8, wherein said horizontal alignment film comprises polyimide, polyamic acid, polymaleimide, or polysiloxane.

10. The liquid crystal display device according to claim 8, wherein the polymer layer, in addition to structures formed by said first and second monomers, has a structure represented by chemical formula (8) in a repeating unit.

11. The liquid crystal display device according to claim 8, wherein the polymer layer, in addition to structures formed by said first and second monomers, includes a structure represented by chemical formula (10) or chemical formula (11) in a repeating unit.

12. The liquid crystal display device according to claim 8, wherein the polymer layer, in addition to structures formed by said first and second monomers, has a structure represented by chemical formula (12) in a repeating unit.

13. The liquid crystal display device according to claim 8, wherein the polymer layer, in addition to structures formed by said first and second monomers, has a structure represented by chemical formula (13) in a repeating unit.

14. The liquid crystal display device according to claim 8, wherein the polymer layer further includes at least one kind of structure selected from chemical formula group (14) in a repeating unit.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an exploded schematic perspective view of a liquid crystal television set of an embodiment according to the present invention.

(2) FIG. 2 is a schematic cross-sectional view of a liquid crystal display panel of an embodiment according to the present invention before a PSA polymerization step.

(3) FIG. 3 is a schematic cross-sectional view of a liquid crystal display panel of an embodiment according to the present invention after a PSA polymerization step.

(4) FIG. 4 is a schematic plan view of a liquid crystal display panel of an IPS mode of an embodiment according to the present invention.

(5) FIG. 5 is a schematic plan view of a liquid crystal display panel of an FFS mode of an embodiment according to the present invention.

(6) FIG. 6 is a graph showing an irradiance spectrum of a light source (blacklight) used in Example 1.

(7) FIG. 7 is a graph showing an absorption spectrum of a monomer represented by a chemical formula (10).

(8) FIG. 8 is a graph showing an irradiance spectrum of a light source (LED light) used in Example 1.

(9) FIG. 9 is a graph showing an absorption spectrum of monomers represented by chemical formulae (12) and (13).

DESCRIPTION OF EMBODIMENTS

(10) The present invention will be mentioned in more detail referring to the drawings in the following embodiments, but is not limited to these embodiments.

(11) The liquid crystal display device of the present invention and a liquid crystal display device prepared by the production method of the present invention can exhibit excellent display characteristics by being used in display devices such as a television, a personal computer, a mobile phone, and an information display.

(12) In the present embodiment, a case where the liquid crystal display device of the present invention or a liquid crystal display device prepared by the production method of the present invention is applied to a television will be described. FIG. 1 is an exploded schematic perspective view of a liquid crystal television set of the present embodiment.

(13) As shown in FIG. 1, a liquid crystal television set 10 of the present embodiment is constituted with a liquid crystal display panel 1, a backlight 2 that provides light to the liquid crystal display panel, and a platform 3 that supports the liquid crystal display panel 1 and the backlight 2. The liquid crystal display panel 1 includes a Thin-Film Transistor substrate (TFT substrate) 11, a Color Filter substrate (CF substrate) 12, and a liquid crystal layer 13 that is sealed between the TFT substrate 11 and the CF substrate 12. A polarizing plate is attached to the surface of the TFT substrate 11 that is opposite to the surface facing the liquid crystal layer 13. In addition, a polarizing plate (all of the polarizing plates are not shown in the drawing) is also attached to the surface of the CF substrate 12 that is opposite to the surface facing the liquid crystal layer 13. Moreover, a retarder may optionally be attached to the polarizing plate. In the back (the opposite side to the display surface of the liquid crystal display panel) of the liquid crystal display panel 1, the backlight 2 is arranged. In addition, in the side or back of the liquid crystal display panel 1, peripherals (not shown in the drawing) such as wiring and drivers for displaying a television image on a display screen are arranged.

(14) The liquid crystal layer 13 is filled with a liquid crystal material having a characteristic in which the liquid crystal material is aligned in a specific direction when a certain degree of voltage is applied thereto. The alignment properties of liquid crystal molecules in the liquid crystal layer 13 are controlled by the application of voltage equal to or higher than a threshold value. The liquid crystal material filled in the liquid crystal layer 13 may have positive or negative anisotropy of dielectric constant.

(15) FIG. 2 is a schematic cross-sectional view of a liquid crystal display panel of the present embodiment, and shows the state before the polymerization (hereinafter, also called “PSA polymerization”) step of the monomer added to the liquid crystal. FIG. 3 is a schematic cross-sectional view of a liquid crystal display panel of the present embodiment, and shows the state after the PSA polymerization step. The TFT substrate 11 includes an insulating transparent substrate 21 formed of a material such as glass, and various wirings, a pixel electrode, TFT, and the like formed on the transparent substrate 21. The CF substrate 12 includes an insulating transparent substrate 31 formed of a material such as glass, and a color filter, a black matrix, a common electrode, and the like formed on the transparent substrate 31.

(16) The TFT substrate 11 includes a horizontal alignment film 22 in the surface contacting the liquid crystal layer, and the color filter substrate 12 includes a horizontal alignment film 32 in the surface contacting the liquid crystal layer. Examples of main components of the horizontal alignment films 22 and 32 include polymer materials such as polyimide, polyamic acid, polymaleimide, and polysiloxane. If alignment treatment such as rubbing treatment or photo-alignment treatment is performed on the surface of the horizontal alignment films 22 and 32, it is possible to specify the pretilt angle of the liquid crystal molecules so as to initially cause the liquid crystal molecules to slant in an approximately horizontal direction. As the photo-alignment material, materials containing compounds including a photoreactive functional group such as a chalcone group, a coumarin group, a cinnamate group, an azobenzene group, or a stilbene group are preferable. As the photo-alignment material, materials containing compounds including a cyclobutane skeleton are also preferable. Examples of the light used for the photo-alignment treatment include polarized UV, unpolarized UV, ion beams, and the like.

(17) Examples of the display mode including the horizontal alignment film include an IPS mode and an FFS mode. A liquid crystal display panel of the IPS mode includes, for example, a pixel electrode 15 and a common electrode 16 as a pair of combteeth-shaped electrodes, as shown in FIG. 4. Moreover, a liquid crystal display panel of the FFS mode includes, for example, a pixel electrode 25 that includes a longitudinal-shaped opening (slit) and a common electrode 26 formed in a planar shape, as shown in FIG. 5.

(18) In the FFS mode, the pixel electrode 25 may be a combteeth-shaped electrode. Moreover, the pixel electrode 25 may be formed in a planar shape, and the common electrode 26 may be an electrode including a longitudinal-shaped opening or may be a combteeth-shaped electrode.

(19) In the present specification, the combteeth-shaped electrode refers to an electrode including plural combteeth and a portion connected to the respective tips of one side of the plural combteeth. The shape of each combtooth is not limited to a linear shape.

(20) The plural linear portions are generally arranged in parallel with each other. The plural linear portions may have a linear shape, or may be formed in a zigzag shape or a V shape.

(21) Before the PSA polymerization step is performed, liquid crystal molecules and one or more kinds of monomers 14 are present in the liquid crystal layer 13. In addition, the monomers 14 start to be polymerized by the PSA polymerization step performed by light irradiation, whereby PSA layers (polymer layers) 23 and 33 are formed on the horizontal alignment films 22 and 32. Moreover, the PSA layers 23 and 33 are preferably formed on one surface of the horizontal alignment films 22 and 32 as shown in FIG. 3. More specifically, the PSA layers 23 and 33 are preferably formed densely with an approximately uniform thickness on one surface of the horizontal alignment films 22 and 32. In addition, the PSA layers 23 and 33 may be formed in a dot shape on the horizontal alignment films 22 and 32. That is, the PSA layers 23 and 33 may be formed in at least a portion of the surface of the horizontal alignment films 22 and 32, and even at this time, it is possible to suppress image sticking while uniformly maintaining the alignment regulating force that the horizontal alignment films 22 and 32 have. Further, the PSA layers 23 and 33 may be formed in at least a portion of the surface of the horizontal alignment films 22 and 32, in a network shape in the entire liquid crystal layer 13. However, in view of suppressing the increase in power consumption, the reduction in contrast, and image sticking in display, the portion where the PSA layers are formed in a network shape is preferably as small as possible.

(22) As a specific procedure, first, a liquid crystal composition containing a liquid crystal material and one or more kinds of monomers 14 is injected between the TFT substrate 11 and the CF substrate 12. Subsequently, a polarizing plate is attached to the TFT substrate 11 and the CF substrate 12 respectively to prepare a liquid crystal display panel, and then the backlight 2 is arranged on the surface of the liquid crystal display panel 1 that is opposite to the display surface thereof. Thereafter, the liquid crystal layer 13 is irradiated with a certain amount of visible light emitted from the backlight 2, thereby polymerizing the monomers 14.

(23) In the present embodiment, the light used in the PSA polymerization step is not particularly limited, and may be, for example, ultraviolet rays or visible light. Particularly, when visible light is used, deterioration or damage of the constitutional members such as the liquid crystal layer and the alignment film can be reduced greatly. Moreover, if visible light is used, the PSA polymerization step can be performed even after the polarizing plate and the backlight are arranged on the liquid crystal display panel. Accordingly, it is not necessary to newly prepare facilities as in the case of performing ultraviolet irradiation, and this greatly contributes to the improvement of efficiency of the production process and the cost reduction.

(24) At least one of the monomers 14 used in the present embodiment causes a chemical reaction alone, can be polymerized by itself, and functions as an initiator for another monomer to cause the polymerization of another monomer. As an example of the polymerization reaction in the present embodiment, a chain polymerization reaction is exemplified in which the radical generated from an initiator function-imparted monomer by light irradiation becomes an active species, and polymerization is caused successively.

(25) When the PSA polymerization step is performed in the present embodiment, there is no particular limitation on the application of voltage to the liquid crystal layer. However, in the case of the IPS or FFS mode, since the initially created horizontal alignment state needs to be fixed, it is preferable to apply a voltage equal to or lower than a threshold voltage at which the liquid crystals respond. In addition, a state where a voltage is practically not applied is more preferable.

(26) Examples of the monomer that is polymerized by functioning as a polymerization initiator for itself by being irradiated with light include compounds represented by the above chemical formula group (8) and compounds represented by the above chemical formula group (9). When the compounds represented by the above chemical formula groups (8) and (9) are mixed with a liquid crystal material, another polymerization initiator does not need to be added thereto, and it is possible to initiate the polymerization reaction by performing only the light irradiation. Particularly, the compounds represented by the above chemical formula group (8) can initiate the polymerization reaction by being irradiated not with ultraviolet rays but with visible light. Accordingly, it is possible to prevent the alignment film itself, the color filter, and the like from being damaged by ultraviolet rays. Moreover, the monomer can be polymerized by using a light emitted from a backlight as visible light, so it is not necessary to make investment in new facilities.

(27) In addition, the compounds represented by the above chemical formula groups (8) and (9) can generate radical by being irradiated with light, even if there is no initiator. Therefore, even if the compounds are used concurrently with other monomers known in the related art that do not cause polymerization reaction alone even being irradiated with light, such as monomers based on acrylate or methacrylate, the PSA layer can be formed. Further, if the monomers represented by the above chemical formula group (9) are used concurrently with the monomers represented by the above chemical formula group (8), it is possible to polymerize the monomers represented by the above chemical formula group (9) by irradiating the monomers not with ultraviolet rays but with visible light.

(28) When the above monomers are polymerized, a polymer including a structure represented by the above chemical formula (1) in a repeating unit is formed, whereby the PSA layers 23 and 33 are formed.

(29) In view of enhancing the alignment regulating force of the horizontal alignment films 22 and 32, it is preferable that R in the above chemical formula (1) includes a structure selected from the above chemical formula group (2).

(30) Moreover, in view of increasing the probability that radical will be generated from the monomer, it is preferable that the PSA layers 23 and 33 include a structure represented by the above chemical formula (3) or (4) in a repeating unit.

(31) Further, in view of further enhancing the alignment regulating force of the horizontal alignment films 22 and 32, it is preferable that Q in the above chemical formula (1) includes a benzene ring structure that is directly bonded to R.

(32) In addition, in view of further strengthening the PSA layers 23 and 33, it is preferable that Q in the above chemical formula (1) includes a polymer chain.

(33) Moreover, in view of further increasing the density of the polymerization starting points in the liquid crystal display panel, it is preferable that the PSA layers 23 and 33 are formed from a bifunctional monomer. It is more preferable that the PSA layers 23 and 33 include at least one kind of structure selected from the above chemical formula group (5) in a repeating unit.

(34) If the PSA layers 23 and 33 are formed by using the above monomers, it is possible to provide a liquid crystal display device that includes a horizontal alignment film, stabilizes liquid crystal alignment by the PSA technique, can suppress the increase in power consumption, reduction in contrast, and image sticking in display, and has long-term reliability.

(35) In embodiment 1, the TFT substrate and CF substrate are not particularly limited, and, for, example, those used in the related art can be used. The material of TFT element is not particularly limited, and, for example, amorphous silicon and the like widely used in the related art can be used. Moreover, for example, an oxide semiconductor showing a high mobility, such as Indium-Galium-Zinc-Oxygen (IGZO), can be used for the TFT element. The TFT element formed of IGZO is suitable for a high-resolution liquid crystal display device since it can be formed in a smaller size, compared to a TFT element formed of amorphous silicon. Accordingly, the TFT element formed of IGZO has drawn attention recently. On the other hand, when rubbing process is applied to such a liquid crystal display device, it is difficult to evenly perform the rubbing treatment on the high-resolution pixels since pile density of the rubbing cloth is limited, and this leads to a concern that the display quality will deteriorate. In this respect, the photo-alignment technique excellent in realizing uniform alignment can be regarded as being useful for commercializing liquid crystal display devices to which the TFT element using an oxide semiconductor such as IGZO is introduced.

(36) However, on the other hand, there is a concern that the oxide semiconductor such as IGZO will cause shift of threshold characteristics of the semiconductor by the ultraviolet irradiation in the photo-alignment technique. The shift of the characteristics leads to the change in the characteristics of the TFT element of pixels and affects the display quality. Moreover, the shift of the characteristics also greatly affects a monolithic driver element that can be formed on a substrate by an oxide semiconductor showing a high mobility. Accordingly, the technique, which can minimize the amount of the irradiated ultraviolet rays of a short wavelength that is necessary for the photo-alignment as described in the present invention, can be regarded as being particularly useful for commercializing the oxide semiconductor such as IGZO.

(37) The liquid crystal display device according to embodiment 1 may be in the form of Color Filter On Array in which a color filter is formed on the TFT substrate 11. In addition, the liquid crystal display device according to embodiment 1 may employ monochrome display or field sequential color system, and in this case, a color filter is not required. For a system requiring a high response speed, such as field sequential color system, IGZO described above is suitable.

(38) If the portion of the liquid crystal display panel of the liquid crystal television set of the present embodiment is disassembled, and Gas Chromatography Mass Spectroscopy (GC-MS) of the liquid crystal composition is performed, the component, weight ratio, and the like of the residual monomer in the liquid crystal composition can be analyzed. Further, if Time-Of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is performed on the surface of the alignment film, the component of the material used for the alignment film can be analyzed.

Example 1

(39) In Example 1, a liquid crystal display panel of the FFS mode was actually prepared. A glass substrate including a planar electrode (common electrode) formed from Indium Tin Oxide (ITO) and a slit electrode (pixel electrode) in the stated order on the surface thereof was prepared and used as a TFT substrate. In addition, a glass substrate including a color filter and BM was prepared and used as a CF substrate. A polyamic acid solution that was used as an alignment film material and contained polyvinyl cinnamate as a photoreactive functional group was coated onto the entire surface of the respective substrates by spin coating. As the glass substrate, #1737 (produced by Corning CO., LTD.) was used. Thereafter, the respective substrates were left under a condition of 90° C. for 1 minute so that the coated solution was temporarily dried. Then the respective substrates were left in a nitrogen atmosphere under a condition of 200° C. for 40 minutes so as to burn the temporarily dried film.

(40) Thereafter, as alignment treatment, the surface of the respective substrates was irradiated with polarized ultraviolet rays of a wavelength of 313 nm at a dosage of 100 mJ/cm.sup.2, in a normal line direction of the respective substrates. In addition, the polarization direction of the polarized ultraviolet rays was set in an azimuth in which an angle of 80° was formed between the ultraviolet rays and the slit electrode of the TFT substrate. Moreover, when being bonded to the TFT substrate, the CF substrate was irradiated with the polarized ultraviolet rays so that the same polarization azimuth is created. In this manner, the alignment film material coated onto the substrates caused a photoisomerization reaction and a photodimerization reaction, whereby a horizontal alignment film having an alignment azimuth forming 10° with respect to the slit electrode was formed.

(41) Subsequently, a thermosetting seal (HC1413FP: produced by Mitsui Chemicals, Inc.) was printed on one substrate by using a screen printing plate. In addition, beads (SP-2035: produced by SEKISUI CHEMICAL CO., LTD.) having a diameter of 3.5 μm were dispersed onto the other substrate. Thereafter, the arrangement of the pair of substrates was adjusted so that the polarization direction of the ultraviolet rays emitted thereto became orthogonal to each other in the respective substrates, and the substrates were bonded to each other.

(42) Next, while being pressurized with a pressure of 0.5 kgf/cm.sup.2, the bonded substrates were heated at 200° C. for 60 minutes in a furnace purged with nitrogen, thereby hardening the seal.

(43) A liquid crystal composition containing a liquid crystal material having positive anisotropy of dielectric constant and a monomer for PSA was injected in vacuum into the cell (the combination of two substrates bonded to each other) prepared in the above method. The monomer was added in an amount of 0.5 wt % based on the weight of the liquid crystal material. In addition, as the liquid crystal material, a liquid crystal material having negative anisotropy of dielectric constant may be used. In this case, if the polarization direction of the polarized ultraviolet rays set in an azimuth forming 10°, the same result is obtained.

(44) The inlet of the cell to which the liquid crystal composition was injected was blocked with an ultraviolet curable resin (TB3026E: produced by Threebond Co., Ltd.) and sealed by being irradiated with ultraviolet rays. The wavelength of the ultraviolet rays was 365 nm, and the pixel portion was shielding so as to be prevented from being affected by the ultraviolet rays as much as possible.

(45) Thereafter, in order to remove the flow alignment of the liquid crystals, the cell was heated at 130° C. for 40 minutes, and realignment treatment was performed to create an isotropic phase of the liquid crystal layer.

(46) Subsequently, a polarizing plate was attached to each of the pair of substrates, thereby completing a liquid crystal display panel of the FFS mode. The polarizing axes of the polarizing plates of both substrates were adjusted so that the polarizing axes became orthogonal to each other.

(47) Next, in order to perform the PSA polymerization step on the liquid crystal display panel, in a state where voltage was not applied, the liquid crystal layer was irradiated with ultraviolet rays from blacklight having a wavelength of around 350 nm as a central wavelength, at a dosage of 2 J/cm.sup.2. In this manner, the monomer in the liquid crystal layer was polymerized. A graph showing an irradiance spectrum of the blacklight is shown in FIG. 6.

(48) In Example 1, a monomer represented by the following chemical formula (10) was used. The compound represented by the following chemical formula (10) is a biphenyl-based bifunctional methacrylate monomer.

(49) ##STR00009##

(50) FIG. 7 is a graph showing an absorption spectrum of a monomer represented by the above chemical formula (10). As shown in FIG. 7, the benzyl-based monomer represented by the above chemical formula (10) mainly absorbs light of a wavelength of 380 nm or shorter. Accordingly, when being irradiated with the ultraviolet rays, the monomer represented by the above chemical formula (10) generates radical as described in the following chemical formulae (11-1) and (11-2), and is polymerized by functioning as a polymerization initiator for itself.

(51) ##STR00010##

(52) As the monomer, monomers based on naphthalene, phenanthrene, or anthracene can be used in addition to the biphenyl-based monomer. In addition, as the polymerizable group, an acryloyloxy group, a vinyl group, a vinyloxy group, an acryloylamino group, an acryloylamino group, or a methacryloylamino group can be used in addition to a methacryloyloxy group. The monomer including these polymerizable groups generate radical by the light of a wavelength ranging from about 300 nm to 380 nm. Therefore, the monomer can be polymerized by functioning as a polymerization initiator for itself.

(53) The performance of the liquid crystal display panel according to Example 1 was evaluated. As a result, the increase in the driving voltage, the reduction in contrast, and the marked reduction in the voltage holding ratio were not observed. In addition, the image sticking thereof was evaluated. A luminance at 2 V (halftone) was measured in advance, and then V of white voltage was continuously applied. 6 hours later, a luminance at 2 V was measured again, and the rate of change was evaluated. The change itself is regarded as image sticking. When the liquid crystal display panel did not contain the monomer, the rate of change was 100% or higher. This means that the alignment regulating force of the alignment film itself is extremely weak. On the other hand, when the liquid crystal display panel contained the monomer and underwent the PSA step, the rate of change could be suppressed to be 5% or lower. That is, an exceptional image sticking-improving effect was obtained.

Example 2

(54) In Example 2, a liquid crystal display panel of the IPS mode was actually prepared. A glass substrate including a pair of combteeth-shaped electrodes (a pixel electrode and a common electrode) formed of Indium Tin Oxide (ITO) on the surface thereof was prepared and used as a TFT substrate.

(55) Thereafter, the liquid crystal display panel of the IPS mode was completed in the same manner as in Example 1, except that the monomer including a composition as described later was used. The polarizing axes of the polarizing plates of both substrates were adjusted so that the polarizing axes became orthogonal to each other.

(56) Subsequently, in order to perform the PSA polymerization step on the liquid crystal display panel, in a state where voltage was not applied, the liquid crystal layer was irradiated with visible light from LED having a wavelength of around 450 nm at a dosage of 5 J/cm.sup.2. In this manner, the monomer in the liquid crystal layer was polymerized. A graph showing an irradiance spectrum of the LED light is shown in FIG. 8.

(57) In Example 2, the monomer represented by the following chemical formula (12) was mixed with the monomer represented by the following chemical formula (13) at a weight ratio of 50:50, and the mixture was added to the liquid crystal material in an amount of 0.5 wt % based on the weight of the liquid crystal material. The compound represented by the following chemical formula (12) is a benzyl-based bifunctional methacrylate monomer, and the compound represented by the following chemical formula (13) is a phenanthrene-based bifunctional methacrylate monomer.

(58) ##STR00011##

(59) FIG. 9 is a graph showing an absorption spectrum of monomers represented by the above chemical formulae (12) and (13). In the present example, the PSA polymerization step is performed by using the LED light passing through the polarizing plate. Accordingly, light of a wavelength shorter than 380 nm is cut by the polarizing plate (left side of the boundary line of 380 nm in FIG. 9). As shown in FIG. 9, the benzyl-based monomer represented by the above chemical formula (12) absorbs light of a wavelength of 380 nm or longer. On the other hand, the phenanthrene-based monomer represented by chemical formula (13) practically does not absorb light of a wavelength of 380 nm or longer. Even in this case, in the present embodiment, the benzyl-based monomer represented by the above chemical formula (12) generates radical functioning as an active species, whereby the phenanthrene-based monomer represented by the above chemical formula (13) is polymerized. In addition, the benzyl-based monomer itself represented by the above chemical formula (12) is also polymerized by the radical, and constitutes a portion of the PSA layer.

(60) As the monomer represented by the above chemical formula (12), monomers based on benzoin ether, acetophenone, benzyl ketal, or ketone that generate radical by photocleavage or hydrogen abstraction can also be used. Moreover, as a polymerizable group imparted to these, an acryloyloxy group, a vinyl group, a vinyloxy group, an acryloylamino group, an acryloylamino group, or a methacryloylamino group can be used in addition to a methacryloyloxy group. The monomer including these polymerizable groups absorb light of a wavelength of 380 nm or longer and generate radical. That is, the monomer can be polymerized by functioning as a polymerization initiator for itself by being irradiated with visible light.

(61) The performance of the liquid crystal display panel according to Example 2 was evaluated. As a result, the increase in the driving voltage, the reduction in contrast, and the marked reduction in the voltage holding ratio were not observed. Further, an exceptional image sticking-improving effect was obtained. Particularly, by employing two-component system, the rate of the polymerization reaction and the rate of the formation of the polymer layer on the alignment film could be optimized. It is considered that for this reason, the formation of a polymer network in the liquid crystal cell could be further suppressed. Moreover, presumably, since the PSA polymerization was performed by using not ultraviolet rays but visible light, the long-term reliability of the liquid crystal display panel of Example 2 might be further improved compared to the liquid crystal display panel of Example 1. Further, even if light irradiation for PSA polymerization is sufficiently performed, the wavelength of the light is greatly different from the sensitivity wavelength (ultraviolet rays) of the photo-alignment film, and accordingly, the photo-alignment state is not damaged.

(62) In Examples 1 and 2, polyvinyl cinnamate was used as the alignment film material. However, materials including a chalcone group, a coumarin group, a stilbene group, an azobenzene group, or the like as a photoreactive functional group can also be used. In addition, polyamic acid, polyimide that is partially or completely imidized, polyamide, siloxane, polymaleimide, and the like can also be used. Moreover, the photoreactive functional group may be appropriately modified with a modifying group. For example, a benzene ring of a cinnamate group may be modified with at least one kind of group selected from a group consisting of fluorine, an alkyl group, an alkoxy group, a benzyl group, a phenoxy group, a benzoyl group, a benzoate group, and a benzoyloxy group. Further, a derivative of the monomer as the alignment film material including the above photoreactive functional group, and a derivative of the monomer as the alignment film material including the above photoreactive functional group containing the above modifying group may be used. If the monomer containing the above modifying group or the above derivative is used, the electric characteristics or alignment stability can be improved.

(63) In Examples 1 and 2, as alignment treatment, the respective substrates were irradiated with polarized ultraviolet rays at a dosage of 100 mJ/cm.sup.2. However, it was confirmed that even with the irradiation energy equal to or smaller than the above, the polymer was sufficiently polymerized, and the alignment stabilization was accomplished. In view of suppressing deterioration caused by the ultraviolet irradiation, the smaller irradiation energy is more preferable. Specifically, it was confirmed that the alignment stabilization was accomplished even at a dosage of 10 mJ/cm.sup.2.

Example 3

(64) In Example 3, a liquid crystal display panel of the IPS mode was actually prepared. A cell was completed in the same manner as in Example 2, except that the alignment film material and the condition of the alignment treatment as described later were used.

(65) As the alignment film material, a polyimide solution including a cyclobutane skeleton was used. The alignment film material was coated onto the substrate and dried in the same manner as in Example 1.

(66) As alignment treatment, the surface of the respective substrates was irradiated with polarized ultraviolet rays of a wavelength of 254 nm at a dosage of 500 mJ/cm.sup.2, in a normal line direction of the respective substrates. In addition, the polarization direction of the polarized ultraviolet rays was set in an azimuth in which an angle of 80° was formed between the ultraviolet rays and the slit electrode. In this manner, the alignment film material coated onto the substrate caused a photodecomposition reaction, whereby a horizontal alignment film was formed.

(67) Thereafter, in the same manner as in Example 1, a liquid crystal compound obtained by adding the monomer represented by the above chemical formula (10) to the liquid crystal material in an amount of 0.5 wt % based on the weight of the liquid crystal material was sealed in the cell, thereby completing the liquid crystal display panel of the IPS mode. As the monomer, the monomers represented by the above chemical formulae (12) and (13) may be used instead of the monomer represented by the above chemical formula (10), in the same manner as in Example 2.

(68) The performance of the liquid crystal display panel according to Example 3 was evaluated. As a result, the increase in the driving voltage, the reduction in contrast, and the marked reduction in the voltage holding ratio were not observed. Moreover, an exceptional image sticking-improving effect was obtained.

Comparative Example 1

(69) A liquid crystal display device of the IPS mode was prepared in the same manner as in Example 3, except that the monomer represented by the above chemical formula (10) was not added into the liquid crystal material, and the PSA polymerization was not performed.

(70) The performance of the liquid crystal display panel according to Comparative example 1 was evaluated. As a result, it was confirmed that sufficient alignment characteristics were not obtained. Presumably, this may be because photodecomposition of the alignment film material was insufficient. It is considered that in order to form an alignment film having sufficient alignment characteristics by using the alignment film material including a cyclobutane skeleton without performing PSA polymerization, ultraviolet irradiation at a dosage of about 2 J/cm.sup.2 needs to be performed. However, if doing so, photodecomposition is also caused in other portions of the alignment film and the color filter, and this leads to a concern that the long-term reliability will be impaired. On the other hand, in the liquid crystal display panel of Example 3, it was confirmed that due to the action of the PSA layer, sufficient alignment characteristics are obtained even if ultraviolet irradiation is performed in such a degree that a problem does not arise in the long-term reliability.

Example 4

(71) In Example 4, a liquid crystal display panel of the IPS mode was actually prepared. A cell was completed in the same manner as in Example 3, except that the method of alignment treatment as described later was used.

(72) As alignment treatment, rubbing treatment was performed on the surface of the respective substrates. The surface was rubbed 3 times with a rubbing cloth of which the pile was allowed to be pushed into the substrate by 0.5 mm. In this manner, a horizontal alignment film was formed on the substrate.

(73) Thereafter, a liquid crystal compound obtained by adding the monomers represented by the above chemical formulae (12) and (13) to the liquid crystal material in an amount of 0.5 wt % based on the weight of the liquid crystal material, was sealed in the cell in the same manner as in Example 2, thereby completing the liquid crystal display panel of the IPS mode. In addition, as the monomer, the monomer represented by the above chemical formula (10) may be used instead of the monomers represented by the above chemical formulae (12) and (13), in the same manner as in Example 1.

(74) The performance of the liquid crystal display panel according to Example 4 was evaluated. As a result, the increase in the driving voltage, the reduction in contrast, and the marked reduction in the voltage holding ratio were not observed. Moreover, an exceptional image sticking-improving effect was obtained.

Comparative Example 2

(75) A liquid crystal display device of the IPS mode was prepared in the same manner as in Example 4, except that the monomers represented by the above chemical formulae (12) and (13) were not added to the liquid crystal material, and PSA polymerization was not performed.

(76) The performance of the liquid crystal display panel according to Comparative example 2 was evaluated. As a result, sufficient alignment regulating force was not obtained, and image sticking was caused markedly. Presumably, this may be because the rubbing strength in the alignment treatment was insufficient. It is considered that in order to form an alignment film having sufficient alignment characteristics by using the alignment film material including a cyclobutane skeleton without performing PSA polymerization, the pile of the rubbing cloth needs to be allowed to be pushed into the substrate by 0.6 mm, and the substrate needs to be rubbed about 5 times so as to increase the rubbing strength. However, doing so results in a concern that the stripe unevenness will cause in the alignment film due to scratch. Moreover, there is a concern that the rubbing cloth or peeled alignment film will become a foreign substance and be mixed into the liquid crystal display panel, and deteriorate the yield. On the other hand, in the liquid crystal display panel of Example 4, it was confirmed that due to the action of the PSA layer, sufficient alignment characteristics was obtained even with a rubbing strength in such a degree that the stripe unevenness and foreign substances were not caused in the alignment film.

(77) The present application claims priority to Patent Application Nos. 2010-231924 filed in Japan on Oct. 14, 2010, 2011-084755 filed in Japan on Apr. 6, 2011, and 2011-177293 filed in Japan on Aug. 12, 2011 under the Paris Convention and provisions of national law in a designated State, the entire contents of which are hereby incorporated by reference.

REFERENCE SIGNS LIST

(78) 1: Liquid crystal display panel 2: Backlight 3: Platform 10: Liquid crystal television set 11: Thin-Film Transistor (TFT) substrate 12: Color Filter (CF) substrate 13: Liquid crystal layer 14: Monomer 15, 25: Pixel electrode 16, 26: Common electrode 21, 31: Transparent substrate 22, 32: Horizontal alignment film 23, 33: PSA layer (polymer layer)