Liquid crystal display device

Abstract

The present invention provides a liquid crystal display device including a horizontal alignment type liquid crystal layer, sub spacers, and a photo-alignment film, wherein the liquid crystal display device can suppress the occurrence of a disclination. The present invention relates to a liquid crystal display device including: a pair of substrates facing each other; and a horizontal alignment type liquid crystal layer interposed between the pair of substrates, wherein at least one of the pair of substrates includes a photo-alignment film, one of the pair of substrates includes multiple sub spacers, the multiple sub spacers are not in contact with the facing substrate under atmospheric pressure, and each of the multiple sub spacers is formed such that its thickness in a cross section monotonically increases and then monotonically decreases from one end to another end of the sub spacer.

Claims

1. A liquid crystal display device comprising: a pair of substrates facing each other; and a horizontal alignment type liquid crystal layer interposed between the pair of substrates, wherein at least one of the pair of substrates includes a photo-alignment film, one of the pair of substrates includes multiple sub spacers, the multiple sub spacers are not in contact with the facing substrate under atmospheric pressure, each of the multiple sub spacers includes a thickness in a cross section which monotonically increases and then monotonically decreases from one end to another end of the sub spacer, the substrate on which the multiple sub spacers are provided further includes multiple main spacers, the multiple main spacers are in contact with the facing substrate under atmospheric pressure, the liquid crystal display device operates with an In-Plane Switching driving mode or a Fringe Field Switching driving mode, each individual one of the multiple main spacers is defined by a single monolithic body, a height of each of the multiple sub spacers is less than a height of each of the multiple main spacers, an alignment film material that forms the photo-alignment film includes at least one photoreactive functional group selected from the group consisting of a chalcone group, a coumarin group, a cinnamato group, an azobenzene group, and a stilbene group, and each of the multiple sub spacers has a bottom diameter of 80% or more and less than 100% of a bottom diameter of each of the multiple main spacers.

2. A liquid crystal display device comprising: a pair of substrates facing each other; and a horizontal alignment type liquid crystal layer interposed between the pair of substrates, wherein at least one of the pair of substrates includes a photo-alignment film, one of the pair of substrates includes multiple sub spacers, the multiple sub spacers are not in contact with the facing substrate under atmospheric pressure, and each of the multiple sub spacers includes a thickness in a cross section which monotonically increases up to a first point, monotonically decreases from the first point to a second point, monotonically increases from the second point to a third point, and then monotonically decreases from the third point, in a range from one end to another end of the sub spacer, an angle defined between a line segment connecting the first point and the second point and a line segment connecting the second point and the third point is at least 168° and less than 180°, the substrate on which the multiple sub spacers are provided further includes multiple main spacers, the multiple main spacers are in contact with the facing substrate under atmospheric pressure, the liquid crystal display device operates with an In-Plane Switching driving mode or a Fringe Field Switching driving mode, and a height of each of the multiple sub spacers is less than a height of each of the multiple main spacers.

3. The liquid crystal display device according to claim 2, wherein an alignment film material to form the photo-alignment film comprises at least one photoreactive functional group selected from the group consisting of a chalcone group, a coumarin group, a cinnamato group, an azobenzene group, and a stilbene group.

4. The liquid crystal display device according to claim 3, further comprising a polymer layer that is formed by polymerization of a monomer contained in the liquid crystal layer and that has an alignment regulating force, on the liquid crystal layer side of the photo-alignment film.

5. The liquid crystal display device according to claim 3, wherein each of the multiple sub spacers has a bottom diameter of 80% or more and less than 100% of a bottom diameter of each of the multiple main spacers.

6. The liquid crystal display device according to claim 2, wherein an alignment film material to form the photo-alignment film includes a cyclobutane skeleton in a repeating unit.

7. The liquid crystal display device according to claim 2, wherein the photo-alignment film includes a main chain structure of at least one polymer selected from the group consisting of polyimides, polyamic acids, polymaleimides, and polysiloxanes.

8. The liquid crystal display device according to claim 2, wherein one of the pair of substrates comprises a color filter.

9. The liquid crystal display device according to claim 2, wherein one of the pair of substrates comprises an IGZO-TFT.

10. The liquid crystal display device according to claim 2, wherein the photo-alignment film is not provided on the multiple sub spacers or has a smaller thickness on the multiple sub spacers than in a portion surrounding the multiple sub spacers.

11. The liquid crystal display device according to claim 2, wherein the substrate on which the multiple sub spacers are provided further comprises a black matrix, the multiple sub spacers and the multiple main spacers are each provided in a dot-shaped manner on the black matrix between sub pixels that are adjacent to each other.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic plan view showing a color filter substrate included in a liquid crystal display device according to Embodiment 1.

(2) FIG. 2 is a schematic cross-sectional view showing a sub spacer included in a liquid crystal display device according to Embodiment 1, and a sub spacer included in a liquid crystal display device according to a comparative embodiment.

(3) FIG. 3 is an enlarged schematic plan view showing two sub spacers and their vicinities in the liquid crystal display device according to Embodiment 1.

(4) FIG. 4 is a schematic cross-sectional view showing a portion of the entire liquid crystal display device, which corresponds to a section taken along line segment B1-B2 in FIG. 1.

(5) FIG. 5 is a schematic plan view showing an active matrix substrate included in the liquid crystal display device of an IPS mode according to Embodiment 1.

(6) FIG. 6 is a schematic plan view showing an active matrix substrate included in the liquid crystal display device of an FFS mode according to Embodiment 1.

(7) FIGS. 7(a) to 7(c) are schematic views showing examples of cross sectional shapes of the sub spacers included in the liquid crystal display device according to Embodiment 1.

(8) FIGS. 8(a) to 8(c) are schematic views showing other examples of cross sectional shapes of the sub spacers included in the liquid crystal display device according to Embodiment 1.

(9) FIGS. 9(a) and 9(b) are schematic views showing still other examples of cross sectional shapes of the sub spacers included in the liquid crystal display device according to Embodiment 1.

(10) FIG. 10 is a graph showing a relationship between the bottom diameter of the sub spacer and the incidence of disclinations.

(11) FIG. 11 is a schematic cross-sectional view showing a sub spacer included in a liquid crystal display device according to Embodiment 2, and the sub spacer included in the liquid crystal display device according to the comparative embodiment.

(12) FIG. 12 is another schematic cross-sectional view of the sub spacer included in the liquid crystal display device according to Embodiment 2.

(13) FIG. 13 is a graph showing a relationship between the angle θ and the incidence of disclinations.

(14) FIG. 14 is an image of a liquid crystal display device in which a disclination is present.

(15) FIG. 15 is a cross-sectional view showing the occurrence of a disclination in the liquid crystal display device according to the comparative embodiment.

(16) FIG. 16 is a schematic plan view showing the occurrence of a disclination in a traverse direction in the liquid crystal display device according to the comparative embodiment.

(17) FIG. 17 is a schematic plan view showing the occurrence of a disclination in a longitudinal direction in the liquid crystal display device according to the comparative embodiment.

DESCRIPTION OF EMBODIMENTS

(18) The present invention will be described below in more detail with reference to the drawings in the following embodiments, but is not limited to these embodiments.

Embodiment 1

(19) With reference to FIGS. 1 to 4, a liquid crystal display device according to Embodiment 1 is described in detail. FIG. 1 is a schematic plan view showing a color filter substrate included in the liquid crystal display device according to Embodiment 1. FIG. 2 is a schematic cross-sectional view of a sub spacer included in the liquid crystal display device according to Embodiment 1 and a sub spacer included in a liquid crystal display device according to a comparative embodiment. The schematic cross-sectional view of a sub spacer included in the liquid crystal display device according to Embodiment 1 shown in FIG. 2 corresponds to a schematic cross-sectional view taken along line segment A1-A2 in FIG. 1. FIG. 3 is an enlarged schematic plan view showing two sub spacers and their vicinities in the liquid crystal display device according to Embodiment 1. Further, FIG. 4 is a schematic cross-sectional view showing a portion of the entire liquid crystal display device, which corresponds to a section taken along line segment B1-B2 in FIG. 1.

(20) As shown in FIG. 1, the color filter substrate included in the liquid crystal display device according to Embodiment 1 is configured such that any one of a red color filter 13R, a blue color filter 13B, and a green color filter 13G is arranged in each subpixel. A black matrix (BM) 4 is arranged at the boundaries of the subpixels, and sub spacers 5 and main spacers 15 are arranged on the BM 4. The sub spacers 5 are arranged on almost all subpixels, except for some subpixels. The main spacers 15 are arranged on the subpixels on which the sub spacers 5 are not arranged. As described, the arrangement is made such that the number of the sub spacers 5 is higher than the number of the main spacers 15. The sub spacers 5 are not in contact with a facing active matrix substrate under atmospheric pressure, whereas the distal ends of the main spacers 15 are in contact with the facing active matrix substrate under atmospheric pressure.

(21) As shown in FIG. 2, the sub spacer 105 included in the liquid crystal display device according to the comparative embodiment has a dent (depressed portion) at its distal end. In contrast, the sub spacer 5 is configured such that, in a cross section (usually, a cross section cutting through the center portion of the sub spacer 5) that is perpendicular to the color filter substrate (substrate main surface), the thickness (height of a point on the profile line) of the sub spacer 5 monotonically increases and then monotonically decreases from one end 5a to another end 5b. In other words, the sub spacer 5 does not have a depressed portion at its distal end. In FIG. 2, the sub spacer 5 is formed in a rounded projecting shape.

(22) In addition, as shown in FIG. 3, the occurrence of an alignment defect that forms a core of a disclination is suppressed at the distal end of the sub spacer 5. Thus, the occurrence of a disclination is suppressed.

(23) As described above, according to one aspect, the present invention provides a liquid crystal display device including a substrate having sub spacers, wherein each sub spacer is formed in a projecting shape having a rounded distal end without a depressed portion at the distal end.

(24) It should be noted that FIG. 3 shows a case where a direction connecting the nearest adjacent sub spacers 5 (left-to-right direction in FIG. 3) is parallel to the initial alignment direction of liquid crystal molecules 8; however, the present embodiment does not impose any particular limitation on the relationship between a direction connecting the nearest adjacent sub spacers 5 and the initial alignment direction of the liquid crystal molecules 8. For example, also in the cases where these directions are perpendicular to each other, and where these directions obliquely intersect each other, the present embodiment can still suppress the occurrence of a disclination.

(25) With reference to FIG. 4, the liquid crystal display device according to Embodiment 1 is described in further detail. The liquid crystal display device according to Embodiment 1 includes a horizontal alignment type liquid crystal layer 30 interposed between a color filter substrate 10 and an active matrix substrate 20 (these substrates correspond to the pair of substrates). The liquid crystal layer 30 includes the liquid crystal molecules 8 (nematic liquid crystal). The color filter substrate 10 includes a transparent insulating substrate 2 such as a glass substrate. The color filters (not shown in FIG. 4) and the BM 4 are formed on the insulating substrate 2, on the side facing the liquid crystal layer 30. The sub spacers 5 and the main spacers (not shown in FIG. 4) are formed on the BM 4. Further, a horizontal photo-alignment film 7 is formed so as to cover these members. It should be noted that although the horizontal photo-alignment film 7 may be provided on the sub spacers 5 as shown in FIG. 4, it is usually not formed on the sub spacers 5 or is formed in minute amount on the sub spacers 5. A linear polarizer 12 is provided on the insulating substrate 2, on the side opposite to the liquid crystal layer 30. The active matrix substrate 20 includes a transparent insulating substrate 1 such as a glass substrate. Various types of wiring, thin film transistors (TFT, not shown in FIG. 4) that function as switching elements, pixel electrodes (not shown in FIG. 4), a common electrode 3, and a horizontal photo-alignment film 6 that covers these members are formed on the insulating substrate 1, on the side facing the liquid crystal layer 30. A linear polarizer 11 is provided on the insulating substrate 1, on the side opposite to the liquid crystal layer 30. The linear polarizers 11 and 12 each may further include a retarder to form a circular polarizer.

(26) The liquid crystal display device according to Embodiment 1 may have a color-filter-on-array structure in which the color filters are provided on the active matrix substrate 20. In addition, the liquid crystal display device according to Embodiment 1 may be a monochrome display. In this case, it is unnecessary to form the color filters. Further, the sub spacers 5 and the main spacers 15 may be formed on the active matrix substrate 20 instead of the color filter substrate 10.

(27) The shapes and arrangement of the pixel electrodes and the common electrode 3 are different depending on the display mode of the liquid crystal display device. FIG. 5 is a schematic plan view showing an active matrix substrate included in the liquid crystal display device of the IPS mode according to Embodiment 1. FIG. 6 is a schematic plan view showing an active matrix substrate included in the liquid crystal display device of the FFS mode according to Embodiment 1. As shown in FIG. 5, for example, in the case of the IPS mode, both of the pixel electrode 23 and the common electrode 3 are combteeth electrodes, and these electrodes are formed on the same layer or different layers. As shown in FIG. 6, in the case of the FFS mode, the pixel electrode 23 and the common electrode 3 are formed on different layers via an insulating layer. One of the electrode 23 and the common electrode 3 is formed with apertures and the other electrode is formed at a certain position so as to cover the apertures. One of these electrodes having apertures is arranged on the upper layer and the other electrode is arranged on the lower layer. In FIG. 6, the pixel electrode 23 is formed with apertures and the common electrode 3 is formed so as to cover the display area including the apertures. Preferably, the apertures are slits.

(28) The display mode of the liquid crystal display device according to Embodiment 1 is not particularly limited to the IPS mode or the FFS mode. The present invention is applicable to other known modes in which the horizontal alignment film is used. For example, an FLC mode and an AFLC mode are also suitable.

(29) Further, as described above, the active matrix substrate 20 includes thin film transistors (TFT) and various types of wiring (for example, gate bus lines, source bus lines, and storage capacitor wiring lines). The pixel electrode 23 and the common electrode 3 can be formed from publicly known materials such as indium tin oxide (ITO) and indium zinc oxide (IZO).

(30) Any material such as amorphous silicon and polysilicon can be used for a semiconductor layer in the TFT included in the active matrix substrate 20. Yet, it is preferred to use an oxide semiconductor having a high mobility, such as indium-gallium-zinc-oxygen (IGZO). The use of IGZO can reduce the size of each TFT element, compared to the case where amorphous silicon is used. Thus, the use of IGZO is suitable for a high-definition liquid crystal display. In particular, IGZO is preferably used in a system for which high response speed is required, as in the case of a field sequential color system.

(31) The method for forming the sub spacer 5 according to Embodiment 1 is not particularly limited, but usually, a photoresist is used to form the sub spacer 5. The type of the photoresist is not particularly limited, and it may be either a positive or negative photoresist. Yet, it is preferred to use a negative photoresist, for example, to obtain a sub spacer diameter (bottom diameter of the sub spacer) that corresponds to a pixel size of a liquid crystal panel for a mobile device. As a result of studies, the present inventors found that in the case where a negative photoresist is used to form the sub spacer, even when the same halftone mask is used, the size of the sub spacer will be different if there are changes in conditions such as the intensity of light to irradiate the mask and the proximity gap. The present inventors also found that in the case where the size (particularly volume) of the sub spacer is small relative to that of the main spacer, the sub spacer tends to shrink due to post-baking, and consequently, the depressed portion is easily formed. Therefore, in order to suppress the formation of the depressed portion, it is important to prevent the sub spacer from becoming too small in size (particularly in volume) relative to the main spacers. The relative size (particularly volume) of the sub spacers can be changed, for example, by a method for changing exposure conditions such as the amount of light exposure, intensity of light to irradiate the mask, proximity gap, and transmittance of the halftone mask. For example, in some cases, shrinkage during post-baking can be suppressed by increasing the transmittance of mesh for a halftone mask used to form the sub spacer and thereby increasing the amount of light exposure. More specifically, for example, Patent Literature 1 discloses the use of a halftone mask having a transmittance of 10 to 15% during formation of alignment controlling protrusions using a negative photoresist; however, in Embodiment 1, the transmittance of a halftone mask used to form the sub spacer 5 is set to 12 to 18% to increase the transmittance, thus increasing the amount of light exposure and improving the shape of a recess. In addition, examples of other methods for ensuring the relative size (particularly volume) of the sub spacer and thus suppressing the formation of the depressed portion include a method for increasing or decreasing the intensity of light to irradiate the mask, and a method for increasing the proximity gap. In the case where a photoresist is used, the corners of the sub spacer 5 will be rounded, not angular.

(32) In addition, the sub spacer 5 is so small that it is difficult to form the horizontal photo-alignment film 7 particularly on its distal end, and thus it is difficult to regulate the alignment particularly at the distal end. Therefore, in view of suppressing a disclination, it is preferred to reduce the area of the upper base of the sub spacer 5, i.e., to approximate the shape of the sub spacer 5 to a projecting shape.

(33) In FIG. 1, the sub spacer 5 has a circular bottom in the plan view of the color filter substrate. Yet, the shape of the bottom of the sub spacer 5 is not particularly limited to the circular shape. For example, the bottom may have a polygonal shape (such as a rhombic or octagonal shape) or an elliptical shape. The absolute size of the bottom of the sub spacer 5 is not particularly limited, but the size of the bottom of the sub spacer 5 relative to that of the main spacer 15 is preferably set as follows: in the case where the sub spacer 5 and the main spacer 15 both have circular bottoms, the bottom diameter of the sub spacer 5 is preferably set to 80% or more of the bottom diameter of the main spacer 15 in view of effectively suppressing the occurrence of a disclination, and is preferably set to 100% or less in view of preventing a reduction in the aperture ratio.

(34) The thickness (height) of the sub spacer 5 is not particularly limited. Yet, the difference in height between the main spacer 15 and the sub spacer 5 is usually 0.2 μm or more and 1 μm or less, and is preferably 0.6 μm.

(35) FIGS. 7 to 9 are schematic views each showing examples of cross sectional shapes of the sub spacers included in the liquid crystal display device according to Embodiment 1. The shape of the sub spacer 5 according to Embodiment 1 is not particularly limited to the one shown in FIG. 2 as long as the thickness (a point on the profile line) of the sub spacer 5 monotonically increases and then monotonically decreases in the cross sectional view. Specifically, for example, the shape may be one having a step as shown in FIG. 7(a), a conical shape as shown in FIG. 7(b), or a cylindrical shape as shown in FIG. 7(c). In the case of the shapes shown in FIGS. 7(a) to 7(c), the distal end of each sub spacer 5 is spherically rounded. In addition, the sub spacer 5 may include a flat portion. Specifically, for example, the cross sectional view of the sub spacer 5 may have a trapezoidal shape as shown in FIG. 8(a), a pyramid-like shape with at least one step as shown in FIG. 8(b), or a cylindrical shape with a flat distal end as shown in FIG. 8(c). Further, the shapes shown in FIGS. 2, 7(a) to 7(c), and 8(a) to 8(c) are all bilaterally symmetrical in the cross sectional view; however, the sub spacer 5 may have a bilaterally asymmetrical and unbalanced shape in the cross sectional view as shown in FIGS. 9(a) and 9(b). All of the shapes shown in FIGS. 7 to 9 can suppress the occurrence of a disclination as in the shape shown in FIG. 2.

(36) The distance between the sub spacers 5 is not particularly limited, and it can be suitably adjusted according to the design (such as the size of the pixel and the subpixel) of the liquid crystal display device. It is considered that the deterioration of the display quality will be more significant if the distance between the sub spacers 5 is long because a large disclination is likely to occur, resulting in the presence of a disclination over several pixels between the sub spacers. In contrast, the present embodiment makes it possible to suppress the occurrence of a disclination even in the case where the distance between the sub spacers 5 is long.

(37) The horizontal photo-alignment films 6 and 7 are formed in the following manner: an alignment film material is diluted in a good or poor solvent to obtain a coating solution; the coating solution is applied to a substrate by ink-jet printing or the like to form a coating film having a thickness of about 1000 to 1500 Å; after application of the coating solution, the thus-obtained coating film is dried and baked; and then the coating film is alignment-treated, for example, by emitting polarized ultraviolet light to the coating film. In the above case where the coating solution containing an alignment film material is applied to the color filter substrate on which the sub spacers 5 are formed, usually, the coating solution hardly remains on the sub spacers 5. Thus, the horizontal photo-alignment film 7 is not formed on the sub spacers 5 or is formed in minute amounts on the sub spacers 5. Yet, as shown in FIG. 4, the horizontal photo-alignment film 7 may be formed on the sub spacers 5.

(38) As for the alignment film material, an alignment film material having a photoreactive functional group is used. The photoreactive functional group includes at least one functional group selected from the group consisting of a chalcone group, a coumarin group, a cinnamato group, an azobenzene group, and a stilbene group. An alignment film material including a cyclobutane skeleton in a repeating unit may also be used. As described above, an isomeric, dimeric, re-aligned, or dissociated alignment film material is used. The liquid crystal layer 30 will have a similar pre-tilt angle (for example, 0°) regardless of which of these materials is used, thus achieving an effect of suppressing a disclination to a similar degree.

(39) Although the present inventors examined whether it is possible to suppress a disclination by increasing the alignment regulating force of the alignment film in the liquid crystal display device according to the comparative embodiment as shown in FIGS. 15 to 17, a sufficient effect was not achieved at this point. The reason was confirmed through observation under an electron microscope as follows: the solution (coating solution) containing an alignment film material, which was applied by inkjet printing, hardly remains particularly in the vicinity of the distal end of each sub spacer, and flows toward the circumference of the bottom of the sub spacer; thus, the alignment film is less likely to be formed particularly in the vicinity of the distal end of the sub spacer, failing to achieve a sufficient alignment regulating force. Therefore, improving the shape of the sub spacer is considered to be effective in the suppression of a disclination.

(40) The liquid crystal display device according to Embodiment 1 may further include a polymer layer having an alignment regulating force on at least one of the horizontal photo-alignment films 6 and 7. The polymer layer is preferably formed entirely on the horizontal photo-alignment films 6 and 7, and more preferably in such a manner that it is dense and has a substantially uniform thickness. In addition, the polymer layer may be formed in a dotted manner on the horizontal photo-alignment films 6 and 7, i.e., it may be formed discretely on the surface of the horizontal photo-alignment films 6 and 7. Also in this case, it is possible to uniformly maintain the alignment regulating force of the horizontal photo-alignment films 6 and 7 and suppress image sticking. Further, after the polymer layer is formed on at least a part of the horizontal photo-alignment films 6 and 7, a polymer network structure formed in a network shape may be formed in the entire liquid crystal layer 30.

(41) An example of a specific procedure for forming the polymer layer is described. First, a liquid crystal composition containing a liquid crystal material and at least one type of monomer is injected between the active matrix substrate 20 and the color filter substrate 10. Subsequently, a polarizer is attached to both of the active matrix substrate 20 and the color filter substrate 10 so as to prepare a liquid crystal display panel, and a backlight is disposed on the liquid crystal display panel, on the side opposite to the display surface. Then, the liquid crystal layer 30 is irradiated with a certain amount of visible light emitted from the backlight.

(42) Light used to polymerize a monomer is not particularly limited, and any light such as ultraviolet light or visible light can be suitably selected according to the type of the monomer. In particular, the use of visible light makes it possible to greatly reduce deterioration or damage that occurs in the constituent members such as the liquid crystal layer and the alignment film. The use of visible light also makes it possible to polymerize a monomer even after the polarizer and the backlight are disposed on the liquid crystal display panel. Therefore, unlike the case of using ultraviolet light for irradiation, there is no need for new equipment, and as a result, the use of visible light greatly contributes to the efficiency of the production process and the cost reduction.

(43) A monomer suitably used to form the polymer layer is described below. The monomer used to form the polymer layer can be determined by confirming the molecular structure of the monomer unit in the polymer layer of the present embodiment.

(44) The polymer layer is preferably formed by polymerization of at least one type of monomer having a monofunctional or polyfunctional polymerizable group having a ring structure. Examples of such monomers include a monomer represented by the following chemical formula (1).
[Chem. 1]
P.sup.1—S.sub.p.sup.1—R.sup.2-A.sup.1-(Z-A.sup.2).sub.m-R.sup.1  (1)

(45) In the chemical formula (1), R.sup.1 represents a —R.sup.2-Sp.sup.1-P.sup.1 group, a hydrogen atom, a halogen atom, a —CN group, an —NO.sub.2 group, an —NCO group, an —NCS group, an —OCN group, an —SCN group, an —SF.sub.5 group, or a C1 to C12 linear or branched alkyl group.

(46) P.sup.1 represents a polymerizable group. Sp.sup.1 represents a C1 to C6 linear, branched, or cyclic alkylene or alkyleneoxy group, or a direct bond.

(47) A hydrogen atom in R.sup.1 may be replaced by a fluorine atom or a chlorine atom. A —CH.sub.2— group in R.sup.1 may be replaced by an —O— group, an —S— group, an —NH— group, a —CO— group, a —COO— group, an —OCO— group, an —O—COO— group, an —OCH.sub.2— group, a —CH.sub.2O— group, an —SCH.sub.2— group, a —CH.sub.2S— group, an —N(CH.sub.3)— group, an —N(C.sub.2H.sub.5)— group, an —N(C.sub.3H.sub.7)— group, an —N(C.sub.4H.sub.9)— group, a —CF.sub.2O— group, an —OCF.sub.2— group, a —CF.sub.2S— group, an —SCF.sub.2— group, an —N(CF.sub.3)— group, a —CH.sub.2CH.sub.2— group, a —CF.sub.2CH.sub.2— group, a —CH.sub.2CF.sub.2— group, a —CF.sub.2CF.sub.2— group, a —CH═CH— group, a —CF═CF— group, a —C≡C— group, a —CH═CH—COO— group, or an —OCO—CH═CH— group, as long as an oxygen atom and a sulfur atom are not adjacent to each other.

(48) R.sup.2 represents an —O— group, an —S— group, an —NH— group, a —CO— group, a —COO— group, an —COO— group, an —O—COO— group, an —OCH.sub.2— group, a —CH.sub.2O— group, an —SCH.sub.2— group, a —CH.sub.2S— group, an —N(CH.sub.3)— group, an —N(C.sub.2H.sub.5)— group, an —N(C.sub.3H.sub.7)— group, an —N(C.sub.4H.sub.9)— group, a —CF.sub.2O— group, an —OCF.sub.2— group, a —CF.sub.2S— group, an —SCF.sub.2— group, an —N(CF.sub.2)— group, a —CH.sub.2CH.sub.2— group, a —CF.sub.2═CH.sub.2— group, a —CH.sub.2CF.sub.2— group, a —CF.sub.2CF.sub.2— group, a —CH═CH— group, a —CF═CF— group, a —C≡C— group, a —CH═CH—COO— group, an —OCO—CH═CH— group, or a direct bond.

(49) A.sup.1 and A.sup.2 are the same or different, and each represents a 1,2-phenylene group, a 1,3-phenylene group, a 1,4-phenylene group, a naphthalene-1,4-diyl group, a naphthalene-1,5-diyl group, a naphthalene-2,6-diyl group, a 1,4-cyclohexylene group, a 1,4-cyclohexenylene group, a 1,4-bicyclo[2.2.2]octylene group, a piperidine-1,4-diyl group, a naphthalene-2,6-diyl group, a decahydronaphthalene-2,6-diyl group, a 1,2,3,4-tetrahydronaphthalene-2,6-diyl group, an indane-1,3-diyl group, an indane-1,5-diyl group, an indane-2,5-diyl group, a phenanthrene-1,6-diyl group, a phenanthrene-1,8-diyl group, a phenanthrene-2,7-diyl group, a phenanthrene-3,6-diyl group, an anthracene-1,5-diyl group, an anthracene-1,8-diyl group, an anthracene-2,6-diyl group, or an anthracene-2,7-diyl group. —CH.sub.2— groups in A.sup.1 and A.sup.2 each may be replaced by an —O— group or an —S— group, as long as they are not adjacent to each other. Hydrogen atoms in A.sup.1 and A.sup.2 each may be replaced by a fluorine atom, a chlorine atom, a —CN group, or a C1 to C6 alkyl, alkoxy, alkyl carbonyl, alkoxy carbonyl, or alkyl carbonyloxy group.

(50) Each Z is the same or different and represents an —O— group, an —S— group, an —NH— group, a —CO— group, a —COO— group, an —OCO— group, an —O—COO— group, an —OCH.sub.2— group, a —CH.sub.2O— group, an —SCH.sub.2— group, a —CH.sub.2S— group, an —N(CH.sub.3)— group, an —N(C.sub.2H.sub.5)— group, an —N(C.sub.3H.sub.7)— group, an —N(C.sub.4H.sub.9)— group, a —CF.sub.2O— group, an —OCF.sub.2— group, a —CF.sub.2S— group, an —SCF.sub.2— group, an —N(CF.sub.3)— group, a —CH.sub.2CH.sub.2— group, a —CF.sub.2CH.sub.2— group, a —CH.sub.2CF.sub.2— group, a —CF.sub.2CF.sub.2— group, a —CH═CH— group, a —CF═CF— group, a —C≡C— group, a —CH═CH—COO group, an —OCO—CH═CH— group, or a direct bond; and m is 0, 1, or 2.

(51) More specific examples thereof include monomers represented by the following chemical formulae (2-1) to (2-5):

(52) ##STR00001##

(53) In these chemical formulae (2-1) to (2-5), each P.sup.1 is the same or different and represents a polymerizable group.

(54) Examples of P.sup.1 above include an acryloyloxy group, a methacryloyloxy group, a vinyl group, a vinyloxy group, an acryloylamino group, and a methacryloylamino group. Herein, hydrogen atoms in benzene rings and fused rings in the compounds represented by the above chemical formulae (2-1) to (2-5) may be partially or fully replaced by halogen atoms, or C1 to C12 alkyl or alkoxy groups. In addition, hydrogen atoms in alkyl and alkoxy groups may be partially or fully replaced by halogen atoms. Further, the bonding position of P.sup.1 to the benzene rings and the fused rings is not limited to the ones shown.

(55) The monomer represented by the chemical formula (1) is a monomer polymerizable by ultraviolet irradiation. The polymer layer of the present embodiment may be a polymerized product of a monomer polymerizable by visible light irradiation.

(56) Monomers to form the polymer layer include two or more types of monomers. The monomer polymerizable by visible light irradiation may be a monomer that polymerizes another monomer. The monomer that polymerizes another monomer refers to, for example, a monomer that undergoes a chemical reaction by visible light irradiation; initiates and promotes polymerization of another monomer that does not polymerize by itself by visible light irradiation; and polymerizes itself, while the wavelength range that induces reaction is different depending on the molecular structure. Owing to the monomer that polymerizes another monomer, a large number of existing monomers that do not polymerize by light irradiation (for example, visible light irradiation) can be used as materials of the polymer layer. Examples of the monomer that polymerizes another monomer include a monomer having a structure that generates radicals by visible light irradiation.

(57) Examples of the monomer that polymerizes another monomer include a monomer represented by the following chemical formula (3).

(58) ##STR00002##

(59) In the chemical formula (3), A.sup.3 and A.sup.4 are the same or different, and each represents a benzene ring, a biphenyl ring, or a C1 to C12 linear or branched alkyl or alkenyl group. At least one of A.sup.3 and A.sup.4 includes an -Sp.sup.2-P.sup.2 group. A hydrogen atom in A.sup.3 and A.sup.4 each may be replaced by an -Sp.sup.2-P.sup.2 group, a halogen atom, a —CN group, an —NO.sub.2 group, an —NCO group, an —NCS group, an —OCN group, an —SCN group, an —SF.sub.5 group, or a C1 to C12 linear or branched alkyl, alkenyl, or aralkyl group. Two adjacent hydrogen atoms in A.sup.3 and A.sup.4 each may be replaced by a C1 to C12 linear or branched alkylene or alkenylene group to form a cyclic structure. A hydrogen atom in an alkyl, alkenyl, alkylene, alkenylene, or aralkyl group in A.sup.3 and A.sup.4 each may be replaced by an -Sp.sup.2-P.sup.2 group. A —CH.sub.2— group in an alkyl, alkenyl, alkylene, alkenylene, or aralkyl group in A.sup.3 and A.sup.4 each may be replaced by an —O— group, an —S— group, an —NH— group, a —CO— group, a —COO— group, an —OCO— group, an —O—COO— group, an —OCH.sub.2— group, a —CH.sub.2O— group, an —SCH.sub.2— group, a —CH.sub.2S— group, an —N(CH.sub.3)— group, an —N(C.sub.2H.sub.5)— group, an —N(C.sub.3H.sub.7)— group, an —N(C.sub.4H.sub.9)— group, a —CF.sub.2O— group, an —OCF.sub.2— group, a —CF.sub.2S— group, an —SCF.sub.2— group, an —N(CF.sub.3)— group, a —CH.sub.2CH.sub.2— group, a —CF.sub.2CH.sub.2— group, a —CH.sub.2CF.sub.2— group, a —CF.sub.2CF.sub.2— group, a —CH═CH— group, a —CF═CF— group, a —C≡C— group, a —CH═CH—COO— group, or an —OCO—CH═CH— group, as long as an oxygen atom, a sulfur atom, and a nitrogen atom are not adjacent to one another.

(60) P.sup.2 represents a polymerizable group. Sp.sup.2 represents a C1 to C6 linear, branched, or cyclic alkylene or alkyleneoxy group, or a direct bond.

(61) Further, n is 1 or 2. A dotted line connecting A.sup.3 with Y and a dotted line connecting A.sup.4 with Y indicate that a Y-mediated bond may be present between A.sup.3 and A.sup.4.

(62) Y represents a —CH.sub.2— group, a —CH.sub.2CH.sub.2— group, a —CH═CH— group, an —O— group, an —S— group, an —NH— group, an —N(CH.sub.2)— group, an —N(C.sub.2H.sub.5)— group, an —N(C.sub.3H.sub.7)— group, an —N(C.sub.4H.sub.9)— group, an —OCH.sub.2— group, a —CH.sub.2O— group, an —SCH.sub.2— group, or a —CH.sub.2S— group, or a direct bond.

(63) More specific examples thereof include monomers represented by the following chemical formulae (4-1) to (4-8).

(64) ##STR00003##

(65) In the chemical formulae (4-1) to (4-8), R.sup.3 and R.sup.4 are the same or different, and each represents an -Sp.sup.2-P.sup.2 group, a hydrogen atom, a halogen atom, a —CN group, an —NO.sub.2 group, an —NCO group, an —NCS group, an —OCN group, an —SCN group, an —SF.sub.5 group, or a C1 to C12 linear or branched alkyl, aralkyl, or phenyl group. At least one of R.sup.3 and R.sup.4 includes an -Sp.sup.2-P.sup.2 group.

(66) P.sup.2 represents a polymerizable group. Sp.sup.2 represents a C1 to C6 linear, branched, or cyclic alkylene or alkyleneoxy group, or a direct bond. When at least one of R.sup.3 and R.sup.4 represents a C1 to C12 linear or branched alkyl, aralkyl, or phenyl group, a hydrogen atom in at least one of R.sup.3 and R.sup.4 above may be replaced by a fluorine atom, a chlorine atom, or an -Sp.sup.2-P.sup.2 group. A —CH.sub.2— group in R.sup.3 and R.sup.4 each may be replaced by an —O— group, an —S— group, an —NH— group, a —CO— group, a —COO— group, an —OCO— group, an —O—COO— group, an —OCH.sub.2— group, a —CH.sub.2O— group, an —SCH.sub.2— group, a —CH.sub.2S— group, an —N(CH.sub.3)— group, an —N(C.sub.2H.sub.5)— group, an —N(C.sub.3H.sub.7)— group, an —N(C.sub.4H.sub.9)— group, a —CF.sub.2O— group, an —OCF.sub.2— group, a —CF.sub.2S— group, an —SCF.sub.2— group, an —N(CF.sub.3)— group, a —CH.sub.2CH.sub.2— group, a —CF.sub.2CH.sub.2— group, a —CH.sub.2CF.sub.2— group, a —CF.sub.2CF.sub.2— group, a —CH═CH— group, a —CF═CF— group, a —C≡C— group, a —CH═CH—COO— group, or an —OCO—CH═CH— group, as long as an oxygen atom, a sulfur atom, and a nitrogen atom are not adjacent to one another.

(67) Examples of P.sup.2 above include an acryloyloxy group, a methacryloyloxy group, a vinyl group, a vinyloxy group, an acryloylamino group, and a methacryloylamino group. Herein, hydrogen atoms in benzene rings in the compounds represented by the above chemical formulae (4-1) to (4-8) may be partially or fully replaced by halogen atoms or C1 to C12 alkyl or alkoxy groups. In addition, hydrogen atoms in alkyl and alkoxy groups may be partially or fully replaced by halogen atoms. Further, the bonding positions of R.sup.3 and R.sup.4 to the benzene rings are not limited to the ones shown.

(68) The monomers to form the polymer layer (for example, the compounds represented by the chemical formulae (2-1) to (2-5), and the compounds represented by the above chemical formulae (4-1) to (4-8)) preferably include two or more polymerizable groups. For example, monomers including two polymerizable groups are preferred.

(69) The above-described monomers may be added to liquid crystal without using a conventional polymerization initiator. This results in a significant improvement in electrical properties because there is no residual polymerization initiator that can be an impurity in the liquid crystal layer. In other words, a polymerization initiator for the monomers can be substantially absent in the liquid crystal layer during polymerization of the monomers.

(70) In the present embodiment, for example, a biphenyl-based bifunctional methacrylate monomer represented by the following chemical formula (5) may be used.

(71) ##STR00004##

(72) In this case, the formation of a polymer can be ensured without mixing a photopolymerization initiator. The radical generation process represented by the following formulae (6-1) and (6-2) is considered to be induced by light irradiation.

(73) ##STR00005##

(74) In addition, the presence of a methacrylate group also allows the monomer to form a polymer by radical polymerization. Monomers that dissolve in liquid crystal are preferably used, and rod-like molecules are preferred. Examples thereof may include naphthalene-based, phenanthrene-based, and anthracene-based monomers, in addition to the biphenyl-based monomer. In addition, hydrogen atoms therein may be partially or fully replaced by halogen atoms, alkyl groups, or alkoxy groups (hydrogen atoms in these groups may be partially or fully replaced by halogen atoms). Examples of polymerizable groups may also include an acryloyloxy group, a vinyloxy group, an acryloylamino group, and a methacryloylamino group, in addition to the methacryloyloxy group. These monomers can generate radicals by light having a wavelength ranging from about 300 to 380 nm. In addition to the above monomers, monomers such as acrylates and diacrylates having no photopolymerization initiating function may be mixed. The photopolymerization reaction rate can be adjusted with these monomers.

(75) In addition, in the present embodiment, a mixture of a monomer represented by the following chemical formula (7-1) and a monomer represented by the following chemical formula (7-2) can also be used.

(76) ##STR00006##

(77) In this case, visible light may be used to irradiate the monomers to induce polymerization, thus reducing damage to the liquid crystal and the photo-alignment films. Other examples of monomers that can be used include benzoin ether-based, acetophenone-based, benzil ketal-based, and ketone-based monomers, which generate radicals by photofragmentation and hydrogen abstraction. A polymerizable group must be attached to these monomers. Examples of the polymerizable group include an acryloyloxy group, a vinyloxy group, an acryloylamino group, and a methacryloylamino group, in addition to the methacryloyloxy group. In addition, in the present embodiment, a polyimide having a cyclobutane skeleton may be used as the main chain of a polymer of an alignment film material.

(78) In addition, a preferred structure in the polymer layer is described in detail. The polymer layer preferably includes a structure represented by the following chemical formula (8) in the repeating unit.

(79) ##STR00007##

(80) In the chemical formula (8), X represents —H or —CH.sub.3; Y represents —O—, —COO—, —CONH—, or a direct bond; R represents a divalent group having a benzene ring structure that is bonded to at least Y; and Q represents a monovalent organic group.

(81) In the present invention, preferably used as the monomer to form the repeating unit is a monomer that itself acts as an initiator and undergoes polymerization by light irradiation. Herein, such a monomer is also referred to as an initiator function-imparted monomer. The monomer preferably has a structure in which an acryloyloxy group, a methacryloyloxy group, a vinyl group, a vinyloxy group, an acryloylamino group, or a methacryloylamino group is bonded to a benzene ring. If the monomer has a structure that forms a repeating unit represented by the above chemical formula (8) (preferably, a structure that includes the benzene ring), radicals can be generated by light irradiation, as shown by the following chemical reaction formula (9), for example. This reaction is considered to be the same as the reaction in which the functional group is cleaved to generate radicals during photo-Fries rearrangement. Further, as shown by the following chemical reaction formula (9), for example, the presence of a methacrylate group allows a radical polymerization reaction to form a polymer. In general, a monomer that is polymerized by light irradiation is referred to as a photopolymerizable monomer. In the case of an initiator function-imparted monomer, the photopolymerizable monomer itself generates radicals and undergoes polymerization, and thus it does not require an initiator. It should be noted that although an initiator may be used to form the polymer layer, the initiator is preferably used in a minimum amount because the residual initiator will affect the performance of the liquid crystal display. It is most preferred not to use an initiator.

(82) ##STR00008##

(83) In the above chemical reaction formula (9), the symbol “*” represents any organic group. The same applies hereinafter.

(84) The above chemical reaction formula (9) shows a mode in which an initiator function-imparted monomer is cleaved by light to generate radicals, and a mode in which a double bond in the monomer is polymerized to form a repeating unit of a polymer.

(85) The initiator function-imparted monomer refers to a monomer that generates radicals and induces a polymerization reaction, even in the absence of a commonly used initiator, by light irradiation using visible light or ultraviolet light whose intensity is comparable to that of ultraviolet light used to irradiate a monomer to induce a polymerization reaction in the usual PSA technique.

(86) Preferably, R in the above chemical formula (8) includes a structure selected from the following chemical formula group (10). If a rod-like skeleton similar to a rod-like liquid crystal molecule and having high affinity with the liquid crystal molecule is included in the repeating unit, it can improve the solubility of the monomer in the liquid crystal and can also enhance the alignment regulating force of the horizontal photo-alignment films.

(87) ##STR00009##

(88) In the chemical formula group (10), hydrogen atoms may be partially or fully replaced by halogen atoms. In addition, each ring structure may be a hetero ring in which a carbon atom is replaced by another atom.

(89) The polymer layer preferably includes a structure represented by the following chemical formula (11) or (12) in the repeating unit.

(90) ##STR00010##

(91) In the chemical formulae (11) and (12), X represents —H or —CH.sub.3; Y represents —O—, —COO—, —CONH—, or a direct bond; and Q represents a monovalent organic group.

(92) In other words, it is preferred that the polymer layer includes a benzoyl skeleton. As shown by the following chemical reaction formula (13), a monomer having a benzoyl skeleton generates radicals by a hydrogen-atom abstraction reaction. Thus, such a monomer is more likely to generate radicals than a monomer having a non-benzoyl skeleton. Therefore, it is possible to reduce the polymerization time required for forming the polymer layer, and also to form a dense polymer layer.

(93) ##STR00011##

(94) Preferably, Q in the above chemical formula (8) includes a benzene ring structure that is bonded to the R moiety. This allows the rod-like skeleton in the repeating unit to become more similar to the rod-like skeleton of the liquid crystal molecule, resulting in an improved affinity between the monomer skeleton and the liquid crystal molecule as well as an enhanced ability of the thus-formed polymer layer to stabilize the liquid crystal alignment. In addition, the liquid crystal is usually sealed within a panel in vacuum; however, if the monomer has a low molecular weight, the concentration of the monomer may unfortunately be reduced or become uneven due to volatilization of the monomer. The introduction of a benzene ring can increase the molecular weight and also reduce the volatility.

(95) Preferably, Q includes a polymer chain. This allows the polymer layer to have a dense three-dimensional structure, thus improving the ability of the polymer layer to stabilize the liquid crystal alignment.

(96) The polymer layer is preferably formed from a bifunctional monomer, and more preferably includes at least one structure selected from the following chemical formula group (14) in the repeating unit. This results in a further increase in the density of polymerization starting points in the liquid crystal display panel. In addition, in the case where cleavage as shown by the above chemical reaction formula (9) is induced to generate radicals, if the monomer is a bifunctional monomer, each of the cleaved moieties will include a polymerization reaction group. Thus, it is possible to suppress the unreacted materials from remaining in the liquid crystal.

(97) ##STR00012##

(98) In the chemical formula group (14), X and X′ each independently represent —H or —CH.sub.3; and Y and Y′ each independently represents —O—, —COO—, —CONH—, or a direct bond.

(99) The average molecular weight of the polymer constituting the polymer layer is not particularly limited, and may be comparable to the number average molecular weight or weight average molecular weight of the polymer formed by the usual PSA technique. Typically, the average molecular weight is desirably 8 or more in terms of the number of repeating units, or 1000 or more in terms of the molecular weight.

(100) In addition to the monomers exemplified above and the polymers including the structures exemplified above, other monomers and polymers that are used in the usual PSA technique can be suitably used in the present invention.

Example 1

(101) A liquid crystal cell (liquid crystal display panel) according to Embodiment 1 was actually produced in Example 1.

(102) First, a 10-inch IGZO-TFT substrate having an FFS structure and a color filter substrate as a counter substrate were provided. Herein, the IGZO-TFT substrate refers to an active matrix substrate in which an indium gallium zinc complex oxide is used as a semiconductor. In addition, a slit electrode on the upper layer was formed to have an electrode width L of 3 μm and to have an inter-electrode distance (slit width) S of 5 μm (L/S=3 μm/5 μm).

(103) As a material of main spacers and sub spacers, a negative photoresist was applied to the color filter substrate, and a mask was arranged. Subsequently, the color filter substrate was irradiated with light having a wavelength of 365 nm and an intensity of 150 mJ/cm.sup.2. A halftone mask having a transmittance of 15% was used to form the sub spacers. The proximity gap between the mask and the color filter substrate was set to 240 μm. Each sub spacer in Example 1 had the same shape as the sub spacer 5 shown in FIG. 2. The sub spacer was formed to have a bottom diameter of 12 μm and a height of 2.5 μm. The height of the main spacer was set such that the thickness of the liquid crystal layer in the active area was 3.3 μm, and the bottom diameter of the main spacer was set to 14 μm. As shown in FIG. 1, the sub spacers were arranged on almost all subpixels, and the main spacers were arranged on the subpixels on which the sub spacers were not arranged. The distance between the nearest adjacent sub spacers was set to 30 μm.

(104) A coating solution containing a photoreactive alignment film material having a photoreactive functional group at the side chain was applied to these substrates by ink-jet printing to form a coating film. After the coating solution was applied, the thus-obtained coating film was temporarily dried at 80° C. for 3 minutes, and then baked at 200° C. for 40 minutes while purging with nitrogen gas. The alignment film on a transparent electrode, which is the uppermost layer (i.e., the layer closest to the liquid crystal layer) on the active matrix substrate, had a film thickness of 45 nm in the active area. The alignment film on the color filter substrate had a film thickness of 50 nm in the active area.

(105) Next, these substrates were irradiated with linearly polarized ultraviolet light having a wavelength of 313 nm and an intensity of 5 J/cm.sup.2 from the normal direction of the substrates for liquid crystal alignment treatment (photo-alignment treatment), whereby a horizontal photo-alignment film was formed. The horizontal photo-alignment film was aligned in a monodomain. In other words, the liquid crystal alignment treatment was performed in a maskless manner, and the domain was not divided.

(106) Next, a thermosetting seal (HC1413FP, manufactured by Mitsui Chemicals, Inc.) was printed on the active matrix substrate by using a screen plate. These two types of substrates were bonded to each other such that the polarization direction of irradiated ultraviolet light is consistent between the substrates. Next, the bonded substrates were heated at 200° C. for 60 minutes in a nitrogen-purged furnace while applying a pressure of 0.5 kgf/cm.sup.2 thereto, and the seal was thus cured.

(107) A liquid crystal material containing liquid crystal molecules having positive anisotropy of dielectric constant was injected under vacuum into a cell prepared by the above method. An inlet of a cell through which the liquid crystal material was injected was sealed with an epoxy adhesive (ARALDITE AR-S30, manufactured by NICHIBAN Co., Ltd.). At this point, a short circuit was created between the electrodes and electrostatic charge was removed from the glass surface so that the liquid crystal alignment would not be disturbed by an external electric field. Next, in order to remove the liquid crystal flow alignment and simulate the curing of the seal in the one drop fill (ODF) process during mass production, the panel was heated at 130° C. for 40 minutes to transform the liquid crystal into the isotropic phase for realignment treatment, whereby obtaining a liquid crystal cell of the FFS mode in which the liquid crystal molecules were uniaxially aligned in a direction perpendicular to the polarization direction of ultraviolet light used to irradiate the alignment film. All the processes were performed under yellow fluorescent light to prevent the liquid crystal panel from being exposed to ultraviolet light emitted from a fluorescent lamp.

Comparative Example 1

(108) In Comparative Example 1, a liquid crystal cell was produced in the same manner as in Example 1, except that the proximity gap was reduced and the intensity of light to irradiate the mask was also reduced to form the sub spacers. Specifically, the proximity gap was set to 100 μm, and the intensity of light having a wavelength of 365 nm in Comparative Example 1 was set to 100% whereas the intensity of light having a wavelength of 365 nm in Example 1 was set to 110%. The shape of the sub spacer in Comparative Example 1 was the same as that of the sub spacer 105 of the comparative embodiment shown in FIG. 2.

(109) The incidence of disclinations was calculated for each of the liquid crystal cells according to Example 1 and Comparative Example 1. The calculation of the incidence of disclinations is the same as the measurement of the so-called yield of the liquid crystal display device. Specifically, a voltage of a threshold or higher was applied to the liquid crystal cell placed between crossed-Nicols polarizers, and the presence of a disclination was visually determined under dark room conditions. The liquid crystal cell in which one or more disclinations were recognized in the display area was evaluated as non-conforming. When 5 out of 100 liquid crystal cells were evaluated as non-conforming, the incidence of disclinations was calculated to be 5%.

(110) Table 1 shows the results. The incidence of disclinations was very high (58.9%) in the liquid crystal cell according to Comparative Example 1, whereas the incidence of disclinations decreased sharply (3.4%) in the liquid crystal cell according to Example 1.

(111) TABLE-US-00001 TABLE 1 Incidence of disclinations Comparative Example 1 58.9% Example 1 3.4%

Modified Example 1

(112) A liquid crystal cell was produced in the same manner as in Example 1, except that the bottom diameter of the sub spacer was set to 11.3 μm, 12 μm, and 12.7 μm independently, and the bottom diameter of every main spacer was set to 15 μm. The incidence of disclinations was measured for each case. FIG. 10 shows the results. FIG. 10 is a graph showing a relationship between the bottom diameter of the sub spacer and the incidence of disclinations.

(113) As shown in FIG. 10, the incidence of disclinations was suppressed to a low level when the bottom diameter of the sub spacer was 12 μm and 12.7 μm. In contrast, the incidence of disclinations increased when the bottom diameter of the sub spacer was 11.3 μm. The reason is considered as follows: if the bottom diameter of the sub spacer is too small relative to the bottom diameter of the main spacer, a portion corresponding to the sub spacer will be exposed to less light while the photoresist is irradiated with light; and as a result, the sub spacer will shrink during post-baking, forming a depressed portion at the distal end of the sub spacer.

(114) As described above, it became clear from Modified Example 1 that when the bottom diameter of the main spacer is 15 μm, the bottom diameter of the sub spacer is preferably 12 μm or more, and the difference in the bottom diameter between the main spacer and the sub spacer is preferably 3 μm or less. In addition, it became clear from Modified Example 1 that the bottom diameter of the sub spacer is preferably 80% or more of the bottom diameter of the main spacer.

Embodiment 2

(115) None of the sub spacers 5 included in the liquid crystal display device according to Embodiment 1 had a depressed portion. In contrast, each of the sub spacers 5 included in a liquid crystal display device according to Embodiment 2 had a depressed portion. Except for the above difference, the liquid crystal display device according to Embodiment 2 is the same as the liquid crystal display device according to Embodiment 1, and thus the description thereof is omitted. In addition, various embodiments described in Embodiment 1 are also suitably applicable to Embodiment 2.

(116) FIG. 11 is a schematic cross-sectional view showing the sub spacer included in the liquid crystal display device according to Embodiment 2, and the sub spacer included in the liquid crystal display device according to the comparative embodiment. As shown in FIG. 11, a sub spacer 205 included in the liquid crystal display device according to Embodiment 2 is configured in the same manner as in the sub spacer 105 included in the liquid crystal display device according to the comparative embodiment such that the thickness (height of a point on the profile line) of the sub spacer 205 in the cross sectional view monotonically increases up to a first point, monotonically decreases from the first point to a second point, monotonically increases from the second point to a third point, and then monotonically decreases from the third point, in a range from an end 205a to another end 205b. In other words, each of the sub spacers 105 and 205 is formed in the shape having a depressed portion at the distal end. More specifically, the cross sectional view refers to a cross section of each of the sub spacers 105 and 205 (usually, a cross section cutting through the center portion of the sub spacers 105 and 205), as in the case of Embodiment 1. In this case, the cross section perpendicular to the color filter substrate (substrate main surface) was observed.

(117) Meanwhile, the depth of the depressed portion of the sub spacer 205 is shallower than that of the sub spacer 105. Specifically, the sub spacer 205 is formed such that the angle θ formed between a line segment connecting the first point and the second point and a line segment connecting the second point and the third point is 168° or more (preferably, 177° or more) and less than 180°.

(118) As described above, the sub spacer 205 is formed such that the depth of the depressed portion is shallow, so that an alignment disturbance, which becomes a core of a disclination, does not easily occur at the depressed portion, and the occurrence of a disclination is thus suppressed.

(119) FIG. 12 is another schematic cross-sectional view of the sub spacer included in the liquid crystal display device according to Embodiment 2. As shown in FIG. 12, provided that a first point “a” has coordinates (X1, Z1) and a second point “b” has coordinates (X2, Z2), when the profile line has a shape that is bilaterally symmetrical about a line extending in the thickness direction of the sub spacer and passing through the second point, the angle θ formed between a line segment connecting the first point “a” and the second point “b” and a line segment connecting the second point “b” and the third point “c” can be calculated from the following formula.
Tan(θ/2)=(X2−X1)/(Z2−Z1)

Example 2

(120) A liquid crystal cell according to Embodiment 2 was produced in Example 2.

(121) A liquid crystal cell of Example 2 was produced in the same manner as in the liquid crystal cell of Example 1, except that the proximity gap was reduced and the intensity of light to irradiate the mask was also reduced to form the sub spacers. Specifically, the proximity gap was set to 100 μm, and the intensity of light having a wavelength of 365 nm in Example 2 was set to 91% whereas the intensity of light having a wavelength of 365 nm in Example 1 was set to 110%. The shape of the sub spacer in Example 2 was the same as that of the sub spacer 205 shown in FIG. 11.

(122) The incidence of disclinations was calculated for each of the liquid crystal cells according to Example 2 and Comparative Example 1. The shape of the sub spacer in Comparative Example 1 was the same as that of the sub spacer 105 of the comparative embodiment shown in FIG. 11, and the angle θ=164°. Table 2 shows the results. The incidence of disclinations was very high (58.9%) in the liquid crystal cell according to Comparative Example 1, whereas the incidence of disclinations was suppressed to a low level (11.4%) in the liquid crystal cell according to Example 2.

(123) TABLE-US-00002 TABLE 2 Incidence of disclinations θ (deg) Comparative Example 1 58.9% 164 Example 2 11.4% 168

Modified Example 2

(124) A liquid crystal cell was produced in the same manner as in Example 2, except that the angle θ was set to 180°, and the incidence of disclinations was measured. FIG. 13 shows the results. FIG. 13 is a graph showing a relationship between the angle θ and the incidence of disclinations.

(125) As shown in FIG. 13, it became clear that the incidence of disclinations was suppressed to a low level with the angle θ of 168° as a threshold.

(126) The aforementioned embodiments may be employed in appropriate combination as long as the combination is not beyond the spirit of the present invention. Each embodiment may also be employed in appropriate combination with the other embodiments.

(127) The present application claims priority to Patent Application No. 2011-262528 filed in Japan on Nov. 30, 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

(128) 1, 2, 101, 102: insulating substrate 3, 103: common electrode 4, 104: black matrix (BM) 5, 105, 205: sub spacer 5a, 5b, 205a, 205b: end 6, 7, 106, 107: horizontal photo-alignment film 8, 108: liquid crystal molecule 10, 110: color filter substrate 11, 12, 111, 112: linear polarizer 13R, 13B, 13G: color filter 15: main spacer 20, 120: active matrix substrate 23: pixel electrode 30, 130: liquid crystal layer a: first point b: second point c: third point