JP6030413B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device having a plurality of openings (slits) in an electrode.

  In a vertical alignment type liquid crystal display device, a technique for improving viewing angle characteristics by providing a plurality of openings in electrodes facing each other across a liquid crystal layer is known (for example, Japanese Patent Application Laid-Open No. 2004-252298). reference). In the liquid crystal display device of this prior example, by providing each opening, it is possible to generate an oblique electric field in a different direction in the liquid crystal layer when a voltage is applied. By forming the alignment domain, the viewing angle dependency due to each other's alignment domain is complemented, and the viewing angle dependency is reduced as a whole.

  In the liquid crystal display device as described above, the response direction of the liquid crystal molecules to the electric field is controlled by an oblique electric field generated near the edge of each opening. This utilizes the phenomenon that liquid crystal molecules near the edge of the opening respond at a lower voltage than liquid crystal molecules in other regions. For this reason, when the liquid crystal display device as described above is multiplex driven in a normally black mode, the liquid crystal molecules near the edge of the opening respond to the electric field at the non-selection voltage (display off voltage). The transmittance of that portion will increase. As a result, the appearance is visually recognized as light leakage near the edge of each opening, leading to a reduction in display quality. Such light leakage becomes more noticeable as the viewing angle is tilted.

JP 2004-252298 A

  A specific aspect of the present invention is to improve display quality in a liquid crystal display device having an opening in an electrode.

A liquid crystal display device according to one aspect of the present invention includes (a) a first substrate and a second substrate which are disposed to face each other, (b) a first electrode provided on one surface side of the first substrate, and (c) a first electrode. A second electrode provided on one surface side of the two substrates; (d) a liquid crystal layer provided between the first substrate and the second substrate; and (e) a first polarizing plate disposed outside the first substrate. And (f) a second polarizing plate disposed outside the second substrate, and (g) an optical compensator disposed between at least one of the first substrate and the first polarizing plate or between the second substrate and the second polarizing plate. comprises, (h) the first electrodes has a first opening plurality of which aligns a long side direction in the first direction, the second electrode may have a plurality of second openings The display portion is configured in a region where the first electrode and the second electrode overlap each other, and the plurality of first openings and the plurality of second openings are in a plan view. Made to be staggered without overlapping is disposed inside of the display unit, (i) the optical compensation plate is a refractive index anisotropy positive its optical axis substantially parallel to the first direction Uniaxial compensator, or nx> when the surface normal direction is the z axis and the refractive index is nz, and the two orthogonal directions in the plane are the x axis and the y axis, and the refractive indexes are nz and ny, respectively. The liquid crystal display device is characterized in that the x-axis is any one of biaxial compensators having a relationship of ny> nz and disposed substantially parallel to the first direction.

  According to the above configuration, when a liquid crystal display device having an opening in an electrode is driven in a multiplex drive in a normally black mode, an increase in transmittance near the edge of the opening at a non-selection voltage (display off voltage) is prevented and crossing is performed. It is possible to reduce the talk and improve the display quality.

  In the above liquid crystal display device, for example, the transmission axes of the first polarizing plate and the second polarizing plate are substantially orthogonal to each other, and each of the transmission axes and the optical axis or the x axis of the optical compensator are approximately 45 °. They are arranged at an angle.

  Thereby, it is possible to further enhance the effect of preventing the increase in transmittance and reducing the crosstalk.

In the liquid crystal display device of the second opening more may be arranged aligned in a second direction that is different from the respective longitudinal first direction. In this case, it is preferable that the sum of a plurality of long side edge of the first opening is set greater than the sum of a plurality of long side edge of the second opening.

  Thereby, it is possible to further enhance the effect of preventing the increase in transmittance and reducing the crosstalk.

  It is also preferable that the plurality of first openings and the plurality of second openings are alternately arranged along a direction orthogonal to the first direction in plan view.

  In the above liquid crystal display device, the retardation value of the uniaxial compensation plate is preferably in the range of 10 nm to 30 nm (more preferably in the range of 10 nm to 30 nm).

  In the above liquid crystal display device, the biaxial compensation plate has an in-plane retardation value (nx-ny) d in the range of 5 nm to 50 nm (more preferably 10 nm), where d is the thickness thereof. It is also preferable that the range is ˜30 nm.

FIG. 1 is a cross-sectional view showing the structure of the liquid crystal display device of the first embodiment. FIG. 2A is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate. FIG. 2B is a plan view showing another example of the structure of the first opening and the second opening. FIG. 3A is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate. FIG. 3B is a plan view showing another example of the structure of the first opening and the second opening. FIG. 4 is a cross-sectional view showing the structure of the liquid crystal display device of the third embodiment. FIG. 5 is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate. FIG. 6 is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing the structure of the liquid crystal display device of the first embodiment. This liquid crystal display device includes a first substrate 11 and a second substrate 12 that are arranged to face each other, and a liquid crystal layer 17 that is arranged between the two substrates as a basic configuration.

  The first substrate 11 and the second substrate 12 are transparent substrates such as a glass substrate and a plastic substrate, respectively. As illustrated, the first substrate 11 and the second substrate 12 are bonded to each other with a predetermined gap (for example, about 4 μm).

  The first electrode 13 is provided on one surface side of the first substrate 11. Similarly, the second electrode 14 is provided on one surface side of the second substrate 12. The first electrode 13 and the second electrode 14 are each configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example. The first electrode 13 is provided with a plurality of first openings (first slits) 18, and the second electrode 14 is provided with a plurality of second openings (second slits) 19. The first openings 18 and the second openings 19 are arranged so as to be staggered without overlapping each other in plan view.

  The alignment film 15 is provided on one surface side of the first substrate 11 so as to cover the first electrode 13. The alignment film 16 is provided on one surface side of the second substrate 12 so as to cover the second electrode 14. As these alignment films 15 and 16, vertical alignment films that restrict the alignment state of the liquid crystal layer 17 to the vertical alignment are used. The alignment films 15 and 16 are not subjected to uniaxial alignment treatment such as rubbing treatment.

  The liquid crystal layer 17 is provided between the first substrate 11 and the second substrate 12. In the present embodiment, the liquid crystal layer 17 is configured using a liquid crystal material having a negative dielectric anisotropy Δε. The refractive index anisotropy Δn of the liquid crystal material is, for example, about 0.15. In the liquid crystal layer 17 of the present embodiment, the alignment direction of the liquid crystal molecules when no voltage is applied is set to a vertical alignment that is substantially perpendicular to the substrate surfaces of the first substrate 11 and the second substrate 12.

  The first polarizing plate 21 is disposed outside the first substrate 11. Similarly, the second polarizing plate 22 is disposed outside the second substrate 12. The 1st polarizing plate 21 and the 2nd polarizing plate 22 are arrange | positioned so that each transmission axis may mutually cross substantially orthogonally.

  The optical compensation plate (viewing angle compensation plate) 23 is disposed between the first substrate 11 and the first polarizing plate 21. The optical compensation plate 23 is a uniaxial compensation plate having a negative refractive index anisotropy and an optical axis in the surface normal direction.

  The optical compensation plate 24 is disposed between the first substrate 11 and the optical compensation plate 23. The optical compensation plate 24 is a uniaxial compensation plate having a positive refractive index anisotropy. Specifically, the optical compensator 24 has an optical axis in its plane, and when the compensator normal direction is defined by the z axis and the compensator plane is defined by the x axis and the y axis orthogonal to each other, This is an optical compensator in which the refractive index nx, the refractive index ny in the y direction, and the refractive index nz in the z direction have a relationship of nz = ny <nx. The optical compensation plate 24 preferably has a retardation value in the range of 5 nm to 50 nm, and more preferably in the range of 10 nm to 30 nm from the viewpoint of viewing angle characteristics, for example, 20 nm in the present embodiment. Set to

  FIG. 2A is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate. As shown in FIG. 2 (A), each first opening 18 has a rectangular outer shape extending in one direction, each longitudinal direction is along the horizontal direction in the figure, and the short direction is the figure. They are arranged along the inside vertical direction. Similarly, each of the second openings 19 has a rectangular outer shape extending in one direction so that each longitudinal direction is along the left-right direction in the drawing and the short side direction is along the up-down direction in the drawing. Is arranged. Further, the first openings 18 and the second openings 19 are alternately arranged one by one without overlapping each other in the vertical direction in the figure.

  Here, the slit length (length in the longitudinal direction) of each first opening 18 and each second opening 19 is set to, for example, about 100 μm. The slit width (length in the short direction) of each first opening 18 and each second opening 19 is set to about 20 μm, for example. The interval between the first openings 18 and the second openings 19 in the longitudinal direction (inter-distance) is preferably equal to or less than the slit width, and is set to about 20 μm, for example. Further, it is desirable that the first openings 18 and the second openings 19 are alternately arranged at regular intervals in a plan view, and the interval between the adjacent first openings 18 and the second openings 19 is, for example, 40 μm. Set to degree.

  Further, as shown in FIG. 2A, the first polarizing plate 21 and the second polarizing plate 22 described above are such that one of the transmission axes 31 and 32 has the first opening 18 and the second opening. 19 is arranged in a 45 ° direction with respect to the longitudinal direction, and the other is arranged in a 135 ° direction. The optical compensator 24 is arranged so that the optical axis 34 is parallel to the longitudinal direction of each first opening 18 and each second opening 19.

  FIG. 2B is a plan view showing another example of the structure of the first opening and the second opening. As shown in the figure, when the region 41 where the first electrode 13 and the second electrode 14 overlap each other forms a display portion expressing a predetermined character or design (in this example, the number “1”), that is, in a segment display type. In some cases, it is desirable that each first opening 18 and each second opening 19 be disposed only within a region 41 corresponding to the display unit. Here, the segment display type means that the region where the electrodes overlap is configured to directly form a character or design to be displayed, and can basically display only a predetermined character or the like. A region having an area ratio of about 50% or less in the effective display region of the apparatus contributes to the display of characters and the like. This is different from a dot matrix display type in which various characters can be freely formed by appropriately combining several pixels from a plurality of regularly arranged pixels having substantially the same shape.

  Next, the result of verifying the effect obtained by the liquid crystal display device of the first embodiment will be described. Here, while producing the liquid crystal display device which employ | adopted the numerical conditions of the example mentioned above as an Example, the liquid crystal display device of a comparative example was produced on the same conditions except having omitted the optical compensator 24, and each liquid crystal display device Was operated by 1/4 duty multiplex drive, and the appearance was observed. As a result, the liquid crystal display device of the example had a beautiful appearance with little crosstalk, and this tendency was particularly remarkable when observed from an oblique direction. In contrast, the liquid crystal display device of the comparative example did not look good due to the occurrence of crosstalk. More specifically, in the liquid crystal display device of the comparative example, when the off segment was observed from an oblique direction, light leakage occurred particularly near the long edge of each opening. Similar observations were made in the liquid crystal display device of the example. As a result, although light leakage occurred in the vicinity of the short edge of each opening, light leakage in the vicinity of the long edge was significantly smaller than that in the comparative example.

  In the above-described embodiment, the optical compensation plate 24 is disposed between the first substrate 11 and the optical compensation plate 23. However, the optical compensation plate 24 is disposed between the first polarizing plate 21 and the optical compensation plate 23. May be. Further, although the optical compensation plates 23 and 24 are arranged only on the first substrate 11 side, they may be further arranged on the second substrate 12 side. One of the optical compensation plate 23 and the optical compensation plate 24 is disposed between the first substrate 11 and the first polarizing plate 21, and the other is disposed between the second substrate 12 and the second polarizing plate 22. Also good. In the above-described embodiment, both the first electrode 13 and the second electrode 14 are each provided with a plurality of openings. However, only one of the electrodes may be provided with a plurality of openings.

(Second Embodiment)
In the liquid crystal display device according to the first embodiment described above, the openings are arranged so that the longitudinal directions of the openings are aligned in one direction. However, the longitudinal lengths of the first opening and the second opening are the same. The directions may be along different directions. The embodiment in this case will be described below. The basic configuration of the liquid crystal display device is the same as that of the first embodiment (see FIG. 1), and the description thereof is omitted here.

  FIG. 3A is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate. As shown in FIG. 3A, each first opening 18 has a rectangular outer shape extending in one direction, each longitudinal direction is along the left-right direction in the figure, and the short direction is the figure. They are arranged along the inside vertical direction. On the other hand, each of the second openings 19 has a rectangular outer shape extending in one direction, each longitudinal direction is along the vertical direction in the drawing, and the short side direction is in the horizontal direction in the drawing. It is arranged along. Further, the first openings 18 and the second openings 19 are alternately arranged one by one without overlapping each other in the vertical direction in the figure. In this example, the slit length of each first opening 18 is set longer than the slit length of each second opening 19.

  As shown in FIG. 3A, the first polarizing plate 21 and the second polarizing plate 22 described above have one of the transmission axes 31 and 32 based on the longitudinal direction of each first opening 18. The 45 ° direction and the other are arranged in the 135 ° direction. The optical compensation plate 24 is arranged so that the optical axis 34 thereof is parallel to the longitudinal direction of each first opening 18. That is, in this example, each first opening 18 has a longer slit length than each second opening 19. Therefore, when viewed as a whole, the long side edges aligned in the horizontal direction in the figure and the vertical direction in the figure. Comparing the proportion of long edges that are aligned, the former is larger. That is, the total slit length of each first opening 18 is larger than the total slit length of each second opening 19. In such a case, it is preferable to make the optical axis 34 of the optical compensation plate 24 parallel to the longitudinal direction of each first opening 18 corresponding to the long side edge having a relatively large ratio (total). Thereby, light leakage near the long edge is suppressed, so that light leakage is further reduced as a whole.

  As in the first embodiment, as shown in FIG. 3B, when the region 41 where the first electrode 13 and the second electrode 14 overlap each other forms a display portion that expresses a predetermined character or design. The first openings 18 and the second openings 19 are preferably arranged only in the area 41 corresponding to the display unit.

(Third embodiment)
In the liquid crystal display devices of the first and second embodiments described above, the optical compensation plate 24 that is a uniaxial compensation plate having a positive refractive index anisotropy and the optical compensation that is a uniaxial compensation plate having a negative refractive index anisotropy. Although the plate 23 is used, an optical compensation plate (so-called biaxial viewing angle compensation plate) having both functions may be used.

  FIG. 4 is a cross-sectional view showing the structure of the liquid crystal display device of the third embodiment. This liquid crystal display device basically has the same configuration as the liquid crystal display device according to the first embodiment described above, and the optical compensators 23 and 24 in the liquid crystal display device according to the first embodiment are compensated for biaxial viewing angles. Only the point of replacement with the plate 25 is different. As illustrated, the viewing angle compensation plate 25 is disposed between the first substrate 11 and the first polarizing plate 21.

  Here, the biaxial viewing angle compensation plate 25 has a refractive index nx in the x direction and a refraction in the y direction when the normal direction of the compensation plate is defined as the z axis and the compensation plate plane is defined by the x axis and the y axis orthogonal to each other. The refractive index ny and the refractive index nz in the z direction have a relationship of nx> ny> nz. In the biaxial viewing angle compensation plate 25, (nx−ny) × (compensation plate thickness) corresponds to the retardation value of the uniaxial compensation plate (optical compensation plate 23) described above. Hereinafter, this retardation value is referred to as “in-plane retardation”. The in-plane retardation value of the biaxial viewing angle compensation plate 25 of the present embodiment is preferably a value in the range of 5 nm to 100 nm, and from the viewpoint of viewing angle characteristics, a value in the range of 20 nm to 50 nm is preferable. Preferably, for example, it can be about 20 nm. In this example, one biaxial viewing angle compensation plate 25 is used, but one more biaxial viewing angle compensation plate may be disposed between the second substrate 12 and the second polarizing plate 22. In that case, it is preferable that the sum of the in-plane retardation values of the two biaxial viewing angle compensation plates meets the numerical conditions described above.

  FIG. 5 is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate. As illustrated, each first opening 18 and each second opening 19 have the same structure as in the case of the first embodiment described above. Further, the transmission axes 31 and 32 of the first polarizing plate 21 and the second polarizing plate 22 are also arranged in the same manner as in the first embodiment. The biaxial viewing angle compensation plate 25 is arranged so that the in-plane refractive index direction 35 (the above-described x direction) is parallel to the longitudinal direction of each first opening 18 and each second opening 19. ing.

  Next, the result of verifying the effect obtained by the liquid crystal display device of the third embodiment will be described. Here, a liquid crystal display device adopting the numerical condition of the above-described example as an example was manufactured, and the appearance was observed by operating by ¼ duty multiplex driving. As a result, the liquid crystal display device of the example had a beautiful appearance with little crosstalk, and this tendency was particularly remarkable when observed from an oblique direction.

(Fourth embodiment)
In the liquid crystal display device according to the third embodiment described above, each opening is arranged so that the longitudinal direction of each opening is aligned in one direction. However, the length of each of the first opening and the second opening is set. The directions may be along different directions. The embodiment in this case will be described below. The basic configuration of the liquid crystal display device is the same as that of the first embodiment, and a description thereof is omitted here.

  FIG. 6 is a plan view showing an example of the structure of the first opening and the second opening and the arrangement conditions of the polarizing plates and the optical compensation plate. As illustrated, each first opening 18 and each second opening 19 have the same structure as that of the second embodiment described above. The transmission axes 31 and 32 of the first polarizing plate 21 and the second polarizing plate 22 are also arranged in the same manner as in the second embodiment. Further, the biaxial viewing angle compensation plate 25 has a long side in which the ratio 35 of the first opening 18 and the second opening 19 is relatively large in the direction 35 in which the in-plane refractive index is large (the above-described x direction). It is preferable that the optical axis 34 of the optical compensation plate 24 be parallel to the longitudinal direction of each first opening 18 corresponding to the edge. Thereby, light leakage near the long edge is suppressed, so that light leakage is further reduced as a whole.

  In addition, this invention is not limited to the content of embodiment mentioned above, In the range of the summary of this invention, it can change and implement variously.

DESCRIPTION OF SYMBOLS 11: 1st board | substrate 12: 2nd board | substrate 13: 1st electrode 14: 2nd electrode 15, 16: Alignment film 17: Liquid crystal layer 18: 1st opening part 19: 2nd opening part 21: 1st polarizing plate 22: Second polarizing plate 23: optical compensator (uniaxial compensator with negative refractive index anisotropy)
24: Optical compensator (uniaxial compensator with positive refractive index anisotropy)
25: Biaxial viewing angle compensation plate 31, 32: Transmission axis of polarizing plate 33: Optical axis 34: Optical axis 35: Direction in which in-plane refractive index is large

Claims (6)

A first substrate and a second substrate disposed opposite to each other;
A first electrode provided on one side of the first substrate;
A second electrode provided on one side of the second substrate;
A liquid crystal layer provided between the first substrate and the second substrate;
A first polarizing plate disposed outside the first substrate;
A second polarizing plate disposed outside the second substrate;
An optical compensation plate disposed between at least one of the first substrate and the first polarizing plate or between the second substrate and the second polarizing plate;
Including
Wherein the first electrodes has a first opening of the plurality disposed aligned long side direction in the first direction,
The second electrode has a plurality of second openings,
The display unit is configured in a region where the first electrode and the second electrode overlap each other,
The plurality of first openings and the plurality of second openings are arranged inside the display unit such that they are staggered without overlapping each other in plan view,
The optical compensator has a positive refractive index anisotropy and an optical axis of the uniaxial compensator arranged substantially parallel to the first direction, or the refractive index of the optical compensator with the surface normal direction as the z axis is nz, When the two orthogonal directions in the plane are the x-axis and the y-axis and the respective refractive indexes are nz and ny, the relationship is nx>ny> nz, and the x-axis is substantially parallel to the first direction. Any of the arranged biaxial compensators,
Liquid crystal display device. The first polarizing plate and the second polarizing plate have their transmission axes substantially orthogonal to each other, and each of the transmission axes and the optical axis or the x axis of the optical compensator form an angle of about 45 °. Arranged so that,
The liquid crystal display device according to claim 1. The plurality of second openings are arranged with their respective longitudinal directions aligned in a second direction different from the first direction ,
The sum of the long side edges of the plurality of first openings is set to be larger than the sum of the long side edges of the plurality of second openings,
The liquid crystal display device according to claim 1. The plurality of first openings and the plurality of second openings are alternately arranged along a direction orthogonal to the first direction in plan view.
The liquid crystal display device according to any one of claims 1 to 3. The uniaxial compensation plate has a retardation value in the range of 5 nm to 50 nm.
The liquid crystal display device according to claim 1. The biaxial compensator has an in-plane retardation value (nx-ny) d in the range of 5 nm to 50 nm, where d is the thickness thereof.
The liquid crystal display device according to claim 1.

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