JP4901541B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a vertical alignment type liquid crystal display device with viewing angle compensation.

  Conventionally, as a viewing angle compensation technique for a vertical alignment type liquid crystal display device, a method using a viewing angle compensation plate having various optical characteristics has been proposed as described below.

Patent Document 1, the three principal refractive indices _{n x,} n y, has a _{n z,} 1 single _{n z} are two other principal refractive indices _n x of which is smaller than _{n y,} the minimum principal refractive It is disclosed to use a viewing angle compensator in which an axis corresponding to the rate _nz is parallel to the surface normal direction of the compensator (having negative refractive index anisotropy). Such a viewing angle compensator is disposed at least one between the liquid crystal cell and the polarizing plates arranged in crossed Nicols on both sides thereof. As the viewing angle compensation plate, equal to the refractive indices n _x and n _y in the plane, a negative uniaxial compensator the optical axis is parallel to the surface normal direction of the viewing angle compensation plate, a so-called C plates or refraction in the plane negative biaxial compensator and the rate n _x and n _y not equal to each other, so-called biaxial plate is used.

  Also in Patent Document 2, a biaxial plate similar to that described in Patent Document 1 is disposed at least between the liquid crystal cell and the polarizing plates arranged in crossed Nicols on both sides thereof. In Patent Document 2, the axis corresponding to the larger main refractive index in the plane of the biaxial plate, that is, the slow axis is substantially parallel or substantially perpendicular to the absorption axis of the adjacent polarizing plate in the display plane. In addition, it is disclosed that it is preferable to dispose a biaxial plate and further to set the in-plane retardation of the biaxial plate to 120 nm or less.

Also in Patent Document 3, a viewing angle compensation plate is arranged at least between the liquid crystal cell and the polarizing plates arranged on both sides thereof in a crossed Nicol arrangement. Patent Document 3 has an optical axis in the plane, the refractive index anisotropy and a positive uniaxial compensator (surface normal direction refractive index n _z, the two in-plane refractive index n _x, n _{As y} , _nz = _ny < _nx ), a so-called A plate and a C plate as described above are combined such that the A plate is disposed on the liquid crystal cell side and the C plate is disposed on the polarizing plate side. Further, it is disclosed that the in-plane retardation of the A plate is preferably 120 nm or less.

  Patent Document 4 discloses a biaxial plate as disclosed in Patent Documents 1 and 2 as a viewing angle compensation means of a vertical alignment liquid crystal display device of a type in which a plurality of liquid crystal regions are aligned in an axially symmetrical manner when a voltage is applied. It is disclosed that it is effective to use a viewing angle compensation member in which an A plate and a C plate are overlapped as disclosed in Document 3.

  Patent Documents 2 to 4 are designed based on the viewing angle compensation principle of the vertical alignment type liquid crystal display device shown in Patent Document 1 so that the conditions of the optical compensation plate are designed so that more effective viewing angle compensation can be performed. is there.

  Patent Document 1 does not limit the product of the birefringence of the liquid crystal material and the cell thickness of the vertical alignment type liquid crystal display device, that is, the retardation range in the cell thickness cross section. Patent Documents 2 to 4 examine the range of retardation within the thickness cross section of the cell. Regarding the retardation in the thickness cross section of the liquid crystal layer, Patent Documents 2 and 3 (both refer to paragraph [0037]) disclose that the thickness is preferably 80 nm or more and 400 nm or less, and Patent Document 4 (Claim 13). Discloses that it is preferably 300 nm or more and 550 nm or less.

  The suitable range of retardation in the thickness cross section of the liquid crystal layer disclosed in Patent Documents 2 to 4 corresponds to an active matrix liquid crystal display device typified by a thin film transistor (TFT) liquid crystal display device (LCD). .

Japanese Examined Patent Publication No. 7-69536 Japanese Patent No. 3330574 Japanese Patent No. 3027805 JP 2000-19518 A

  Some vertical alignment type liquid crystal display devices perform segment display and are driven in a simple matrix. The retardation in the thickness cross section of the liquid crystal layer of such a vertical alignment type liquid crystal display device is desirably larger than that of the active matrix liquid crystal display device from the viewpoint of satisfactory on / off operation. A particularly effective viewing angle compensation technique is desirable for a vertical alignment type liquid crystal display device having a liquid crystal cell having a large retardation in the thickness section.

  An object of the present invention is to provide a liquid crystal display device that has a vertical alignment type liquid crystal cell that is driven in a simple matrix and can perform good viewing angle compensation even when the retardation in the thickness cross section of the liquid crystal cell is large. Is to provide.

  According to an aspect of the present invention, a first polarizing plate, a vertical alignment type liquid crystal cell disposed above the first polarizing plate, and a first biaxial layer disposed above the liquid crystal cell. A simple matrix comprising a plate, a second biaxial plate disposed above the first biaxial plate, a second polarizing plate disposed above the second biaxial plate, and the liquid crystal cell And the first and second polarizing plates are arranged in a substantially orthogonal Nicols positional relationship, and when a driving voltage is applied to the liquid crystal cell, the liquid crystal molecules in the liquid crystal layer The pretilt angle is imparted to the liquid crystal molecules so that the tilting direction of the liquid crystal is at an angle of approximately 45 ° with both the absorption axis of the first polarizing plate and the absorption axis of the second polarizing plate within the display surface. In the display plane, the slow axis in the plane of the second biaxial plate is The second biaxial plate is arranged so as to be substantially parallel to the absorption axis of the second polarizing plate, and the slow axis in the plane of the first biaxial plate is the second biaxial plate. There is provided a liquid crystal display device in which the first biaxial plate is disposed so as to be substantially orthogonal to the slow axis in the plane.

  Two biaxial plates are arranged on one side of the liquid crystal cell. A biaxial plate in which the in-plane slow axis of the biaxial plate on the polarizing plate side is substantially parallel to the absorption axis of the polarizing plate, and the in-plane slow axis of the biaxial plate on the liquid crystal cell side is arranged on the polarizing plate side Is substantially perpendicular to the in-plane slow axis. Thereby, even if the retardation in the thickness cross section of the liquid crystal cell is large, it becomes easy to compensate for the retardation, and further, the deterioration of the display quality in a deep viewing angle range is suppressed.

  A liquid crystal display device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to a first embodiment. Between the back polarizing plate 10 and the front polarizing plate 11, a vertical alignment type liquid crystal cell 20 is disposed. Note that the backlight is disposed, for example, on the outer side (the lower side of the drawing) of the rear polarizing plate 10.

  The configuration of the liquid crystal cell 20 will be described. A lower transparent electrode 22 is formed on the upper surface of the lower transparent substrate 21, and a lower alignment film 23 is formed on the upper surface of the lower transparent electrode 22. An upper transparent electrode 27 is formed on the lower surface of the upper transparent substrate 28, and an upper alignment film 26 is formed on the lower surface of the upper transparent electrode 27. The liquid crystal layer 25 is sandwiched between the lower alignment film 23 and the upper alignment film 26 facing each other, and the sealing material 24 seals the liquid crystal layer 25. The diameter of the gap control material that determines the cell thickness is 4 μm.

  As the lower and upper alignment films 23 and 26, for example, a vertical alignment film SE-1211 manufactured by Nissan Chemical Industries, Ltd. is used. By rubbing the lower and upper alignment films 23 and 26 with, for example, a rayon rubbing cloth, a pretilt angle θ is given so that the liquid crystal molecules M fall down in the rubbing direction.

  As the liquid crystal layer 25, for example, a liquid crystal material manufactured by Merck Co., Ltd. having a birefringence Δn of 0.15 and a negative dielectric anisotropy (liquid crystal molecules are tilted from the vertical direction by applying a voltage) is used. Since the cell thickness is 4 μm and the birefringence Δn is 0.15, the retardation in the thickness section of the liquid crystal cell 20 is 600 nm. The liquid crystal cell 20 has a positive retardation within the thickness cross section.

  The liquid crystal cell 20 performs segment display and is driven in a simple matrix at a high duty ratio (1: N, where N is 4 or more). The lower and upper transparent electrodes 22 and 27 have a pattern corresponding to the display pattern, and are connected to the control device 40. The control device 40 supplies a drive signal and controls the display state.

  In the simple matrix drive, when the duty ratio increases, the ratio of the on voltage to the off voltage decreases. Therefore, in order to perform a good on / off operation, the change in transmittance must be steep with respect to the voltage change.

  In a vertical alignment type liquid crystal cell, a change in transmittance with respect to a change in voltage can be made steep by increasing the retardation in the thickness section. The retardation in the thickness cross section can be increased by increasing the thickness of the liquid crystal layer and / or increasing the birefringence Δn of the liquid crystal material.

  In a vertical alignment type liquid crystal cell that performs simple matrix driving with a high duty ratio (N is 4 or more), the retardation in the thickness section is preferably larger than 550 nm, and more preferably 555 nm or larger. In addition, there is no upper limit in particular in the retardation in the thickness cross section of a liquid crystal cell.

  Examples of display that performs segment display by simple matrix drive include 7-segment display (character shape 8), audio display (display of setting state including frequency), and air conditioner display (setting state including temperature). Display), odd trip display (distance) in the car meter, and the like.

  A viewing angle compensation member in which two biaxial plates 30 and 31 are stacked is inserted between the liquid crystal cell 20 and the front polarizing plate 11.

Each of the biaxial plates 30 and 31 has a refractive index in the surface normal direction (a direction parallel to the normal direction of the display surface of the liquid crystal cell 20) of the three main refractive indexes, _nz, and in-plane (liquid crystal when the two indices of refraction in a plane parallel to the display surface of the cell 20) was _{n x} and _{n y,} it satisfies the relationship of _{n x> n y> n z} .

Each of the biaxial plates 30 and 31 has a negative retardation of 205 nm in the thickness cross section. Magnitude of retardation in the thickness cross section of the biaxial plate, the average value of the two refractive indices n _x and n _y in a plane _{(n x + n y) /} 2 and the surface normal direction of the refractive index n _z Is multiplied by the thickness of the biaxial plate.

The in-plane retardations of the biaxial plates 30 and 31 are 60 nm, respectively. The size of the retardation in the plane of biaxial plate, the difference between one of the refractive indices n _x and the other refractive index n _y in the plane, is calculated by multiplying the thickness of the biaxial plate.

  As the back polarizing plate 10 and the front polarizing plate 11, those having a structure in which a film serving as a polarizer is protected by a triacetyl cellulose (TAC) film are used. The TAC film contained in each polarizing plate has a negative retardation with a size of about 60 nm in the thickness cross section.

  The combined member of the biaxial plates 30 and 31, the rear polarizing plate 10, and the front polarizing plate 11 has a negative retardation with a size of 530 nm (205 nm + 205 nm + 60 nm + 60 nm) in the thickness cross section.

  In this way, the retardation in the thickness cross section of the member including the biaxial plates 30 and 31, the rear polarizing plate 10, and the front polarizing plate 11 is positive or negative with respect to the retardation in the thickness cross section of the liquid crystal cell. On the other hand, by making the absolute value close, retardation in the thickness cross section of the liquid crystal cell can be compensated.

  Next, referring to FIG. 2, the absorption axis direction of the back polarizing plate 10, the rubbing direction of the lower and upper alignment films of the liquid crystal cell 20, the slow axis direction of the biaxial plates 30 and 31, and the front polarizing plate 11 will be described. FIG. 2 is a schematic view of the liquid crystal display device of the first embodiment, in which schematic plan views of constituent members such as the back polarizing plate 10 are arranged in the order of arrangement in the thickness direction.

  Absorption axis directions D10 and D11 of the rear polarizing plate 10 and the front polarizing plate 11 are substantially orthogonal to each other in the display surface. That is, the back polarizing plate 10 and the front polarizing plate 11 are arranged in a substantially orthogonal Nicols arrangement. A case where the angle formed by the two directions is in the range of 80 ° to 100 ° is referred to as being substantially orthogonal.

  In the liquid crystal cell 20, the rubbing direction D23 of the lower alignment film 23 and the rubbing direction D26 of the upper alignment film 26 are antiparallel to each other. Both the rubbing directions D23 and D26 form an angle of approximately 45 ° with respect to both the absorption axis directions D10 and D11 of the polarizing plates 10 and 11 in the display surface. That is, in the display surface, the direction in which the liquid crystal molecules fall when a driving voltage is applied and the absorption axis of both polarizing plates form an angle of about 45 °. The range of 35 ° to 55 ° is referred to as approximately 45 °.

Plane slow axis direction D31 (direction corresponding to the maximum refractive indices n _x in the plane) of the biaxial plate 31 of the front polarizing plate 11 side, in the display plane, substantially the absorption axis direction D11 of the front polarizer 11 Parallel. The case where the angle between the two directions is in the range of −10 ° to 10 ° is referred to as substantially parallel.

  Further, the in-plane slow axis direction D30 of the biaxial plate 30 on the liquid crystal cell 20 side is substantially orthogonal to the in-plane slow axis direction D31 of the biaxial plate 31 in the display surface.

  The biaxial plate described above is produced by stretching a film made of an organic resin. The C plate used in the second embodiment to be described later is produced in the same manner. Examples of organic resins used for the biaxial plate and the C plate include polyethylene, polypropylene, polynorbornene, polyvinyl chloride, cellulose ester, polystyrene, acrylonitrile-butadiene-styrene copolymer resin (ABS resin), and acrylonitrile-styrene copolymer resin. (AS resin), polymethyl methacrylate, polyvinyl acetate, polyvinylidene chloride, polyamide, polyacetal, polycarbonate, modified polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, poly Examples include arylate, liquid crystal polymer, polyamideimide, polyimide, and polytetrafluoroethylene.

  Stretching is currently widely used as a method for producing biaxial plates and C plates. However, with such a manufacturing method, the size of the retardation within one thickness section of the biaxial plate and the C plate can be increased only to about 270 nm at the maximum. In consideration of the stable mass production of the biaxial plate, the maximum retardation is about 250 nm.

  As described above, the retardation in the thickness cross section of the liquid crystal cell is preferably larger than 550 nm. Therefore, in order to compensate for such retardation of the liquid crystal cell, two or more viewing angle compensators are used as in this embodiment.

  The biaxial plate and the C plate are commercially available, for example, for viewing angle compensation of an active matrix liquid crystal display device (vertical alignment type TFT-LCD) having a vertical alignment type liquid crystal cell. The retardation in the thickness cross section of the commercially available biaxial plate and C plate is about 90 to 250 nm, and for the biaxial plate, the in-plane retardation is 40 nm to 120 nm, especially 40 nm to 70 nm is widely used. It has been.

  Although it is considered that the in-plane retardation of the biaxial plate can be 40 nm or less, it is difficult to stably control the in-plane retardation to 40 nm or less. Biaxial plates are not commercially available.

  In particular, many biaxial plates are in circulation for vertical alignment TFT-LCDs (for example, liquid crystal televisions). It is desirable in terms of cost to use a viewing angle compensator with a large circulation amount or use the same kind of viewing angle compensator. The apparatus of the above embodiment uses two biaxial plates of the same type (thus, the retardation in the thickness section and the retardation in the plane are equal).

  Next, liquid crystal display devices according to first and second comparative examples will be described. The first and second comparative examples are the same as the first embodiment in that two biaxial plates are arranged between the liquid crystal cell and the front polarizing plate. The direction of the slow axis is different from that of the first embodiment. The size of the retardation (in the thickness section and in the plane) of the biaxial plate is the same as in the first embodiment.

  10 and 11 are schematic views of the liquid crystal display devices of the first comparative example and the second comparative example, respectively, showing schematic plan views of constituent members such as the rear polarizing plate 10 arranged in the order of arrangement in the thickness direction. FIG.

  First, a first comparative example will be described with reference to FIG. The apparatus of the first comparative example is different from the apparatus of the first embodiment in the direction of the in-plane slow axis of the biaxial plate on the front polarizing plate 11 side. The biaxial plate 131 on the front polarizing plate 11 side is arranged so that the in-plane slow axis direction D131 is orthogonal to the absorption axis direction D11 of the front polarizing plate 11 in the display surface. The in-plane slow axis direction D30 of the biaxial plate 30 on the liquid crystal cell 20 side and the in-plane slow axis direction D131 of the biaxial plate 131 on the front polarizing plate 11 side are parallel to each other in the display surface. .

  Next, a second comparative example will be described with reference to FIG. The apparatus of the second comparative example is the same as the apparatus of the first embodiment, the direction of the in-plane slow axis of the biaxial plate on the front polarizing plate 11 side, and the in-plane retardation of the biaxial plate on the liquid crystal cell 20 side. The direction of the phase axis is different. As in the first comparative example, the biaxial plate 131 on the front polarizing plate 11 side is arranged so that the in-plane slow axis direction D131 is orthogonal to the absorption axis direction D11 of the front polarizing plate 11 in the display surface. Has been. Further, the biaxial plate 130 on the liquid crystal cell 20 side is arranged so that the in-plane slow axis direction D130 is orthogonal to the in-plane slow axis direction D131 of the biaxial plate 131 in the display surface.

  Next, a liquid crystal display device according to a third comparative example will be described with reference to FIG. FIG. 12 is a schematic view of a liquid crystal display device of a third comparative example in which schematic plan views of components such as the back polarizing plate 10 are arranged in the order of arrangement in the thickness direction. The third comparative example differs from the first embodiment in that one biaxial plate is disposed on each side of the liquid crystal cell 20. The size of the retardation (in the thickness section and in the plane) of the biaxial plate is the same as in the first embodiment.

  The in-plane slow axis direction D130a of the biaxial plate 130a disposed between the back polarizing plate 10 and the liquid crystal cell 20 is orthogonal to the absorption axis direction D10 of the back polarizing plate 10 in the display surface. An in-plane slow axis direction D131 of the biaxial plate 131 disposed between the liquid crystal cell 20 and the front polarizing plate 11 is orthogonal to the absorption axis direction D11 of the front polarizing plate 11 in the display surface.

  In the first embodiment, the in-plane slow axis of the biaxial plate adjacent to the front polarizing plate is parallel to the absorption axis of the front polarizing plate in the display surface. In any of the first to third comparative examples, the in-plane slow axis of the biaxial plate adjacent to the front polarizing plate is orthogonal to the absorption axis of the front polarizing plate in the display surface.

  Next, viewing angle characteristics of the liquid crystal display devices of the first embodiment and the first to third comparative examples will be described with reference to FIG. FIG. 3 is a graph showing the viewing angle characteristics of the black base transmittance when no voltage is applied. The horizontal axis shows the left and right background observation angle in degrees, and the vertical axis shows the transmittance in%. Curves A1, B1 to B3 are viewing angle characteristics of the first example and the first to third comparative examples, respectively.

  About all of a 1st Example and the 1st-3rd comparative example, the transmittance | permeability tends to increase, so that it becomes a deep viewing angle in the left-right direction. However, the degree of increase is the smallest in the examples. In the embodiment, the viewing angle at which the transmittance starts to rise clearly is as large as about 50 ° for both the left and right sides. As described above, the black display at a deep viewing angle is best performed by the apparatus of the embodiment. The difference between the example and both comparative examples is remarkable when the viewing angle is in the range of about 20 ° or more on both the left and right sides.

  As explained above, between the liquid crystal cell and one polarizing plate, the in-plane slow axis of the biaxial plate on the polarizing plate side is parallel to the absorption axis of the adjacent polarizing plate in the display surface, and the liquid crystal By arranging two biaxial plates so that the in-plane slow axis of the biaxial plate on the cell side is orthogonal to the in-plane slow axis of the biaxial plate on the polarizing plate side in the display surface, Good viewing angle characteristics can be obtained.

  Next, a liquid crystal display device according to a second embodiment will be described with reference to FIG. The second embodiment has a larger retardation in the thickness cross section of the liquid crystal cell than the first embodiment. Correspondingly, in addition to the two biaxial plates, the second embodiment has one C plate. The configuration other than the retardation in the thickness cross section of the liquid crystal cell and the added C plate is the same as in the first embodiment.

  FIG. 4 is a schematic view of the liquid crystal display device of the second embodiment in which schematic plan views of constituent members such as the back polarizing plate 10 are arranged in the order of arrangement in the thickness direction. In the second embodiment, the cell thickness is 5.5 μm, the birefringence Δn of the liquid crystal material is 0.15, and the retardation in the thickness cross section of the liquid crystal cell 20a is 825 nm. As the liquid crystal material, for example, a product manufactured by Merck & Co., Inc. can be used.

  The rubbing directions D23a and D26a of the lower alignment film and the upper alignment film of the liquid crystal cell 20a are approximately 45 with respect to both of the absorption axis directions D10 and D11 of the polarizing plates 10 and 11 that are antiparallel to each other and arranged in a crossed Nicols arrangement. It has an angle of °.

Similar to the first embodiment, two biaxial plates 30 and 31 are arranged between the liquid crystal cell 20a and the front polarizing plate 11. A C plate 32 is disposed between the rear polarizing plate 10 and the liquid crystal cell 20a. Among the three main refractive indexes, the C plate 32 has a refractive index in the surface normal direction (direction parallel to the normal direction of the display surface of the liquid crystal cell 20a) as _nz, and is in-plane (the display surface of the liquid crystal cell 20a). two refractive index of a plane parallel) when the _{n x} and _{n y,} satisfies the relationship of _{n x = n y> n z} .

The C plate 32 has a negative retardation of 220 nm in the thickness cross section. In addition, the size of the retardation in the thickness cross section of the C plate depends on the difference between the in-plane refractive index _nx (= _ny ) and the refractive index _{nz in the} surface normal direction. It is calculated by multiplying.

  The combined member of the two biaxial plates 30 and 31, the C plate 32, the rear polarizing plate 10, and the front polarizing plate 11 has a negative retardation with a size of 750 nm (205 nm + 205 nm + 220 nm + 60 nm + 60 nm) in the thickness cross section. .

  Since the retardation of the liquid crystal cell is larger than that of the first embodiment, the apparatus of the second embodiment compensates for this, as in the first embodiment, between the liquid crystal cell and one polarizing plate. In addition to the two biaxial plates arranged, a C plate is arranged between the liquid crystal cell and the other polarizing plate to increase the retardation of the viewing angle compensation member. If necessary, a C plate may be disposed between the liquid crystal cell and the biaxial plate on the liquid crystal cell side.

  Next, the viewing angle characteristics of the liquid crystal display device of the second embodiment will be described with reference to FIG. FIG. 5 is a graph showing viewing angle characteristics of black base transmittance when no voltage is applied. The horizontal axis shows the left and right background observation angle in degrees, and the vertical axis shows the transmittance in%. Also in the second embodiment, as in the first embodiment, the viewing angle at which the transmittance starts to increase clearly is as large as about 50 ° for both the left and right, and the increase in the transmittance at a deep viewing angle is suppressed. .

  Next, a liquid crystal display device according to a third embodiment will be described with reference to FIG. In the third embodiment, the retardation of the liquid crystal cell is larger than that in the second embodiment. Correspondingly, in addition to the two biaxial plates, the third embodiment has two C plates. The configuration other than the retardation in the thickness cross section of the liquid crystal cell and the added C plate is the same as in the second embodiment.

  FIG. 6 is a schematic view of the liquid crystal display device of the third embodiment in which schematic plan views of constituent members such as the back polarizing plate 10 are arranged in the order of arrangement in the thickness direction. In the third embodiment, the cell thickness is 6.9 μm, the birefringence Δn of the liquid crystal material is 0.15, and the retardation in the thickness section of the liquid crystal cell 20b is 1035 nm. As the liquid crystal material, for example, a product manufactured by Merck & Co., Inc. can be used.

  The rubbing directions D23b and D26b of the lower alignment film and the upper alignment film of the liquid crystal cell 20b are approximately 45 with respect to both the absorption axis directions D10 and D11 of the polarizing plates 10 and 11 that are antiparallel to each other and arranged in a crossed Nicols arrangement. It has an angle of °.

  Similar to the first and second embodiments, two biaxial plates 30 and 31 are disposed between the liquid crystal cell 20 b and the front polarizing plate 11. Similar to the second embodiment, a C plate 32 is disposed between the rear polarizing plate 10 and the liquid crystal cell 20a. Further, a C plate 33 is disposed between the C plate 32 and the liquid crystal cell 20b. The C plate 33 has a negative retardation with a size of 220 nm in the thickness cross section.

  A member in which the two biaxial plates 30 and 31 and the two C plates 32 and 33, the rear polarizing plate 10, and the front polarizing plate 11 are combined has a negative thickness of 970 nm (205 nm + 205 nm + 220 nm + 220 nm + 60 nm + 60 nm) in the thickness cross section. Of retardation.

  The apparatus of the third embodiment has a larger retardation of the liquid crystal cell than that of the second embodiment. Therefore, a plurality of C plates are stacked to increase the retardation of the viewing angle compensation member. The C plate to be added may be arranged between the liquid crystal cell and the biaxial plate on the liquid crystal cell side as necessary (C plates may be arranged on both sides of the liquid crystal cell). A stack of a plurality of C plates may be disposed between the liquid crystal cell and the biaxial plate on the liquid crystal cell side.

  Next, the viewing angle characteristics of the liquid crystal display device of the third embodiment will be described with reference to FIG. FIG. 7 is a graph showing the viewing angle characteristic of the black base transmittance when no voltage is applied. The horizontal axis shows the left and right background observation angle in degrees, and the vertical axis shows the transmittance in%. In the third embodiment as well, as in the first and second embodiments, the viewing angle at which the transmittance starts to rise clearly is as large as about 50 ° on both the left and right sides, and the increase in transmittance at a deep viewing angle is suppressed. Has been.

  Next, a liquid crystal display device according to a modification of the third embodiment will be described with reference to FIG. FIG. 8 is a schematic view of the liquid crystal display device of this modification, in which schematic plan views of constituent members such as the back polarizing plate 10 are arranged in the order of arrangement in the thickness direction.

  In the third embodiment, instead of stacking two C plates, one optical plate 32a having a retardation (440 nm) equal to that in the thickness cross section is arranged instead of stacking two C plates. The other configuration is the same as that of the third embodiment.

  The optical plate 32a is made of a cholesteric liquid crystal polymer having a twist pitch shorter than the visible wavelength. It is known that the optical plate having such a structure performs an optical function equivalent to that of the C plate. By appropriately setting the birefringence of the cholesteric liquid crystal and the thickness of the liquid crystal layer, it is possible to produce a viewing angle compensation plate having a large retardation that cannot be obtained by stretching an organic resin such as a norbornene resin. It is. Such an optical plate may also be disposed between the liquid crystal cell and the biaxial plate on the liquid crystal cell side.

  The viewing angle characteristic of the black base transmittance when no voltage is applied in the present modification substantially matches that of the third embodiment (see FIG. 7).

  As described above, when the retardation in the thickness section of the vertical alignment type liquid crystal cell is large, two biaxial plates are arranged between the liquid crystal cell and one polarizing plate on the polarizing plate side. A biaxial plate in which the in-plane slow axis of the biaxial plate is substantially parallel to the absorption axis of the polarizing plate, and the in-plane slow axis of the biaxial plate arranged on the liquid crystal cell side is arranged on the polarizing plate side. By disposing it so as to be substantially orthogonal to the in-plane slow axis, a liquid crystal display device having good viewing angle characteristics can be obtained.

  If the retardation in the thickness cross section of the liquid crystal cell cannot be sufficiently compensated using two biaxial plates, add a C plate to increase the retardation in the thickness cross section of the viewing angle compensation member. Is effective. Note that the C plate can be disposed on either side of the liquid crystal cell, and a plurality of the C plates may be stacked. When arrange | positioning on the same side as a biaxial plate, it arrange | positions to the liquid crystal cell side rather than a biaxial plate. For example, an optical plate made of cholesteric liquid crystal can also be used as the C plate, in addition to those produced by stretching an organic resin.

  In the above embodiment, a biaxial plate having a thickness cross section of 205 nm and an in-plane retardation of 50 nm was used. In order to investigate a suitable range of the in-plane retardation of the biaxial plate, an apparatus in which the in-plane retardation of the biaxial plate was varied in the same configuration as in the first example was manufactured. In-plane retardation was set to 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, and 140 nm in addition to 50 nm.

  When the display of these devices was observed visually, those with in-plane retardation of 40 nm, 50 nm, and 60 nm are excellent in viewing angle characteristics including color change, and those with 120 nm and 140 nm have a wide viewing angle range. The color change and transmittance increase were observed, and the quality was poor. The ones of 80 nm and 100 nm were inferior in quality as compared with those of 40 nm to 60 nm, but were within an allowable range. From the above, it was found that the in-plane retardation of the biaxial plate is preferably 100 nm or less, and more preferably 60 nm or less.

  The liquid crystal display device of the above embodiment can perform good display in a wide viewing angle range from a shallow viewing angle to a deep viewing angle. Such a liquid crystal display device is suitable for, for example, a display panel of an in-vehicle device such as a car audio or a display panel of office equipment such as a copying machine or a facsimile. In the above-described embodiment, the direction in which the viewing angle characteristic is particularly good has been described as the left-right direction. However, this may be the vertical direction as necessary.

  FIG. 9A schematically shows an example of a display panel of an in-vehicle device such as a car audio. Since the display panel P of this example is disposed between the driver seat and the passenger seat, the display panel P can be viewed from a driver seat and a passenger seat at a deep viewing angle. In FIG. 9A, the line of sight when the display panel P is viewed from the driver's seat is indicated by an arrow D1, and the line of sight when viewed from the passenger seat is indicated by an arrow D2.

  FIG. 9B schematically shows an example of a display panel of an office machine such as a copying machine or a facsimile. Such office equipment may be operated by a tall person or a short person, for example. The viewing angle at which the display panel P is viewed can vary greatly depending on the height. In FIG. 9B, the line of sight when the tall person views the display panel P is indicated by an arrow D1, and the line of sight when viewed from a short height is indicated by the arrow D2.

  In addition to using the liquid crystal display device in a state where the biaxial plate is disposed on the side closer to the observer with respect to the liquid crystal cell, the state in which the biaxial plate is disposed on the side farther from the observer with respect to the liquid crystal cell. A liquid crystal display device can also be used.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

FIG. 1 is a schematic sectional view of a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is a schematic view of the liquid crystal display device of the first embodiment, in which schematic plan views of constituent members such as a back polarizing plate are arranged in the order of arrangement in the thickness direction. FIG. 3 is a graph showing the viewing angle characteristics of the black base transmittance when no voltage is applied, in the liquid crystal display devices of the first example and the first to third comparative examples. FIG. 4 is a schematic view of the liquid crystal display device of the second embodiment in which schematic plan views of constituent members such as a back polarizing plate are arranged in the order of arrangement in the thickness direction. FIG. 5 is a graph showing the viewing angle characteristics of the black base transmittance when no voltage is applied in the liquid crystal display device of the second embodiment. FIG. 6 is a schematic view of the liquid crystal display device of the third embodiment in which schematic plan views of constituent members such as a back polarizing plate are arranged in the order of arrangement in the thickness direction. FIG. 7 is a graph showing the viewing angle characteristics of the black base transmittance when no voltage is applied in the liquid crystal display device of the third embodiment. FIG. 8 is a schematic view of a liquid crystal display device according to a modification of the third embodiment, in which schematic plan views of constituent members such as a back polarizing plate are arranged in the order of arrangement in the thickness direction. 9A is a schematic diagram illustrating an example of a display panel of an in-vehicle device such as a car audio, and FIG. 9B is a schematic diagram illustrating an example of a display panel of an office device such as a copying machine or a facsimile. is there. FIG. 10 is a schematic view of a liquid crystal display device of a first comparative example in which schematic plan views of constituent members such as a back polarizing plate are arranged in the order of arrangement in the thickness direction. FIG. 11 is a schematic view of a liquid crystal display device of a second comparative example in which schematic plan views of constituent members such as a back polarizing plate are arranged in the order of arrangement in the thickness direction. FIG. 12 is a schematic view of a liquid crystal display device of a third comparative example in which schematic plan views of constituent members such as a back polarizing plate are arranged in the order of arrangement in the thickness direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Back polarizing plate 11 Front polarizing plate 20 Liquid crystal cell 21 Lower transparent substrate 22 Lower transparent electrode 23 Lower alignment film 24 Sealing material 25 Liquid crystal layer 26 Upper alignment film 27 Upper transparent electrode 28 Upper transparent substrate M Liquid crystal molecule θ Pretilt angle 30, 31 Biaxial plate 32 C plate 40 Control device

Claims (6)

A first polarizing plate;
A vertically aligned liquid crystal cell disposed above the first polarizing plate;
A first biaxial plate disposed above the liquid crystal cell;
A second biaxial plate disposed above the first biaxial plate;
A second polarizing plate disposed above the second biaxial plate;
A controller for driving the liquid crystal cell in a simple matrix,
The first and second polarizing plates are arranged in a substantially orthogonal Nicol positional relationship,
When a driving voltage is applied to the liquid crystal cell, the direction in which the liquid crystal molecules in the liquid crystal layer are tilted is, in the display surface, both the absorption axis of the first polarizing plate and the absorption axis of the second polarizing plate. A pretilt angle is given to the liquid crystal molecules so as to form an angle of about 45 °,
In the display plane, the second biaxial plate is arranged so that the slow axis in the plane of the second biaxial plate is substantially parallel to the absorption axis of the second polarizing plate, Liquid crystal display in which the first biaxial plate is arranged so that the slow axis in the plane of the first biaxial plate is substantially orthogonal to the slow axis in the plane of the second biaxial plate apparatus.   The liquid crystal display device according to claim 1, wherein an in-plane retardation of the first biaxial plate and an in-plane retardation of the second biaxial plate are each 100 nm or less.   The liquid crystal display device according to claim 1, wherein the first and second biaxial plates have the same retardation in the thickness cross section and the same in-plane retardation.   The liquid crystal display device according to claim 1, wherein the biaxial plate is made by stretching a film made of an organic resin.   Furthermore, it has any C plate arrange | positioned at least one between the said 1st polarizing plate and the said liquid crystal cell, and between the said liquid crystal cell and the said 1st biaxial plate. 2. A liquid crystal display device according to item 1.   The liquid crystal display device according to claim 1, wherein the liquid crystal cell includes a liquid crystal layer having a retardation in a thickness cross section of greater than 550 nm.

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