JP2008165043A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element of VA mode which has a wide viewing angle and has an improved display irregularity characteristic. <P>SOLUTION: In the liquid crystal display element 1 of VA mode, a λ/4 plate 5 is arranged between a liquid crystal cell 2 and a polarizing plate 4, and a retardation layer including two retardation plates 6, 7 having a retardation larger than λ/4 is arranged between a polarizing plate 3 and the liquid crystal cell 2. Each of the λ/4 plate 5 and respective retardation plates 6, 7 are arranged such that the optical axis becomes parallel or vertical to the direction of pretilt angle of a liquid crystal layer of the liquid crystal cell 2. The liquid crystal display element 1 is constituted such that the sum of retardation values of the whole retardation plates of which the optical axes become parallel to the formation direction of the pretilt angle of the liquid crystal layer is equal to the sum of retardation values of the whole retardation plates of which the optical axes become vertical to the formation direction of the pretilt angle of the liquid crystal layer among the λ/4 plate 5 and respective retardation plates 6, 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display element, and more particularly to a VA mode liquid crystal display element that can be used for in-vehicle applications such as information display terminals and speedometers.

  In general, a transmissive liquid crystal display element includes an extremely thin liquid crystal layer of about several μm oriented in a predetermined direction, a pair of transparent thin substrates that sandwich the liquid crystal layer, and a polarizer that sandwiches the substrate. And a pair of polarizing plates constituting the analyzer. Here, an electrode patterned in a predetermined shape is formed on the substrate surface on the side where the liquid crystal layer is provided. When a voltage is applied to the liquid crystal layer through this electrode, the alignment of the liquid crystal changes, and the amount or wavelength of light transmitted through the liquid crystal display element changes. Thereby, a desired display can be performed.

  Thus, the liquid crystal display element has a relatively simple structure. In addition, since it is easy to reduce the thickness and weight by selecting components, and it is possible to drive at a low voltage, in recent years, not only for consumer use such as a flat-screen TV and a portable information terminal, but also for example, speed It is also actively used as an in-vehicle display element for meter applications.

  The liquid crystal display element is classified into several modes based on the initial alignment state of the liquid crystal layer and the operation state and alignment state when a voltage is applied. For example, VA (Vertical Alignment) mode is used for so-called in-vehicle liquid crystal display elements such as liquid crystal televisions, portable video equipment viewers, and instrument panels of vehicles such as automobiles (see, for example, Patent Documents 1 and 2). .) The VA mode is a mode with excellent visibility since it has a high contrast ratio when viewed from the front and a wide viewing angle.

  In the VA mode, a liquid crystal layer having a negative dielectric anisotropy (Δε) whose initial alignment state is substantially perpendicular to the substrate (vertical alignment) is sandwiched between a pair of substrates. It is comprised by pinching with a pair of polarizing plate arrange | positioned so that Nicole may be comprised. When a voltage is applied to the liquid crystal layer through the electrode formed on the substrate surface, the alignment of the liquid crystal changes, and the liquid crystal layer is perpendicular to the electric field, that is, the alignment direction of the liquid crystal is parallel to the substrate. Thereby, the light transmission characteristics determined by the product (Δn · d) of the refractive index anisotropy (Δn) of the liquid crystal and the liquid crystal layer thickness (d) between the portion where the voltage is applied and the portion where the voltage is not applied, , There will be a difference in color. By utilizing this difference, a desired display can be performed.

Japanese Patent Laid-Open No. 5-113561 JP-A-10-123576

  As described above, in the VA mode, when no voltage is applied, the liquid crystal layer is oriented substantially perpendicular to the pair of substrates that sandwich the liquid crystal layer. Therefore, a good black display is obtained in the viewing angle direction parallel to the normal direction of the liquid crystal cell, the contrast ratio is high when viewed from the front, and the viewing angle is wide. For this reason, the use of flat panel televisions and portable information terminals as information display elements and the use of so-called in-vehicle devices such as instrument panels for vehicles such as automobiles are being actively studied.

  However, in the VA mode, a problem may occur depending on the electrode structure of the display element to be applied. In other words, there are various types of liquid crystal display elements, such as a dot display method that can handle high-density information display, and a structure that supports segment display including character display that can take into account the design of your choice. On the other hand, when the VA mode is to be applied, display unevenness, that is, display non-uniformity may occur due to the structure of the electrode which is the main configuration.

  FIG. 3 is a schematic cross-sectional view of a VA mode liquid crystal cell. A mechanism for generating an oblique electric field that causes display unevenness will be described with reference to FIG.

  Normally, as shown in FIG. 3, the VA mode liquid crystal cell 100 includes a liquid crystal layer 101 made of a liquid crystal having negative dielectric anisotropy, and includes electrode layers 102 and 103 and a pretilt angle of a predetermined angle. The surface is sandwiched between a pair of substrates (not shown) that have been subjected to an alignment process including a rubbing process so as to achieve substantially uniform vertical alignment.

  In order to display an image, when a voltage is applied between the electrode 102 and the electrode 103 constituting the pixel with the liquid crystal layer 101 interposed therebetween so as to cause an alignment change operation in the liquid crystal layer 101, the liquid crystal layer 101 is Electric fields 104 and 105 schematically shown are formed. At this time, if the structures or areas of the electrode 102 and the electrode 103 are different, an oblique electric field (hereinafter referred to as an oblique electric field) 105 is provided between the peripheral portions of the electrode 102 and the electrode 103 in addition to a desirable vertical electric field 104. May be formed. The oblique electric field 105 causes display unevenness in the VA mode described above.

  A display unevenness generation mechanism in the VA mode will be described with reference to FIGS.

  FIG. 4A shows the direction of rubbing treatment performed in the process of forming the electrode 103 and the liquid crystal cell 100 constituting the liquid crystal cell 100, that is, the direction of pretilt angle formation in the liquid crystal layer (not shown) (arrow 106 in the figure). FIG.

  As shown in FIG. 4A, an arrow 106 which is a pretilt angle forming direction of the liquid crystal layer due to the rubbing treatment direction by applying an electric field for driving the liquid crystal layer to the electrode 103, that is, a desired direction in design. The liquid crystal tries to tilt in the direction of.

  FIG. 4B is a diagram for explaining the relationship between the electrode 103 and the direction of an oblique electric field (arrow 107 in the figure) generated by applying an electric field for driving the liquid crystal layer.

  As shown in FIG. 4B, an oblique electric field is generated in the periphery of the electrode 103 in the direction of the arrow 107 toward the center, and the action of an electric field that attempts to change the orientation of the liquid crystal according to the direction acts on the electrode 103.

  FIG. 4C is a diagram schematically illustrating a generation mechanism of display unevenness that occurs in the liquid crystal cell 100.

  In the liquid crystal cell 100, an electric field in the direction derived from the mechanism described in FIG. 4A and an electric field in the direction derived from the mechanism described in FIG. 4B are simultaneously applied to the liquid crystal layer by application of the electric field. . As a result, as shown in FIG. 4C, the action of the added electric field is applied to the liquid crystal layer.

  In FIG. 4C, in the lower part of the electrode 103, the direction 106 of the pretilt angle and the direction 107 of the oblique electric field coincide with each other, and no problem occurs. However, in other parts, for example, the peripheral part near the center, an electric field in a direction slightly deviated from the desired pretilt angle forming direction is applied to the liquid crystal layer. In the upper portion of the electrode 103, an electric field in the direction derived from the action described in FIG. 4A and an electric field in the opposite direction resulting from the action described in FIG. 4B are simultaneously applied. As a result, the intensity of the electric field in the pretilt angle direction corresponding to the desired liquid crystal operation direction is reduced, or an electric field effect in the direction opposite to the pretilt angle direction corresponding to the desired liquid crystal operation direction is applied to the liquid crystal layer. Become.

  For this reason, in a certain part around each pixel of the liquid crystal cell constituted by the electrodes, a desired balance is obtained by balancing the effect of the alignment change caused by the oblique electric field and the alignment regulating force by the rubbing process that determines the pretilt angle formation direction. The liquid crystal is oriented in a direction deviating from the pretilt angle forming direction (in the example of FIG. 4C, an oblique direction deviating from the vertical direction). For this reason, the liquid crystal cell is a pair of polarized lights arranged so that the crossing angle between the absorption axis of one polarizing plate and the absorption axis of the other polarizing plate is 90 ° ± 5 °, that is, crossed Nicols. In a conventional VA mode liquid crystal display element that is sandwiched between plates, the direction of change in the orientation of the liquid crystal may coincide with or be orthogonal to one of the absorption axes of the upper and lower polarizing plates when a voltage is applied. . In the pixel region of the liquid crystal cell in which the liquid crystal is oriented in this way, the light that should be transmitted is blocked, and it is viewed as a low-brightness display portion, that is, as a black display unevenness, causing display non-uniformity. was there.

  As a cause of the occurrence of display unevenness as described above, there is an electrode structure that sandwiches a liquid crystal layer in the VA mode. This will be described with reference to FIGS.

  FIG. 5 is a plan view schematically showing the main part of a conventional VA mode liquid crystal display element. This liquid crystal display element is a passive matrix type liquid crystal display element having a configuration in which a liquid crystal layer is sandwiched between striped upper and lower electrodes so as to correspond to dot display.

  The conventional VA mode 110 shown in FIG. 5 includes a segment electrode 111 made of a stripe electrode that sandwiches a liquid crystal layer (not shown), and a common electrode 112 similarly made of a stripe electrode. An oblique electric field is always generated in the overlapping portion of the electrode 111 and the electrode 112 constituting the pixel. As a result, the aforementioned display unevenness may be a problem.

  FIG. 6 is also a plan view schematically showing a main part of a conventional VA mode liquid crystal display element. However, unlike this liquid crystal display element, this liquid crystal display element is a passive matrix type liquid crystal having a structure in which a liquid crystal layer is sandwiched between upper and lower electrodes of a desired shape so as to correspond to segment display including character display that can take into account a desired design. It is a display element.

  The conventional segment display VA mode 120 shown in FIG. 6 includes a segment electrode 121 made of an electrode having a desired shape for sandwiching a liquid crystal layer (not shown) and a common electrode 122 of the same type. In addition, since the segment electrode 121 and the common electrode 122 are originally provided at the overlapping position, the segment electrode 121 should not be shown in the plan view. However, in FIG. 6, the segment electrodes 121 are illustrated by shifting them for the sake of explanation.

  Between the electrode wiring 123 of the segment electrode 121 and the common electrode 122, and between the electrode wiring 124 of the common electrode 122 and the segment electrode 121, there is a difference in shape due to the presence or absence of the electrode wirings 123 and 124, and an oblique electric field is generated. appear. As a result, the aforementioned display unevenness may be a problem.

  Further, in the production of the liquid crystal cell, it is difficult to superimpose the upper and lower substrates, and thus the electrodes having the same shape (in the example of FIG. 6, the segment electrode 121 and the common electrode 122) at the same position. May occur. In that case, an oblique electric field is generated in the shifted portion. As a result, the aforementioned display unevenness may be a problem.

  Such a problem of display unevenness can also occur in an active drive type VA mode liquid crystal display device.

  FIG. 7 is a plan view schematically showing the main part of a conventional VA mode liquid crystal display element. This liquid crystal display element is an active matrix liquid crystal display element having a configuration in which each pixel portion includes a TFT (Thin Film Transistor) so as to correspond to dot display.

  In the conventional VA mode 130 shown in FIG. 7, a liquid crystal layer (not shown) is sandwiched between the solid plate-like counter electrode 131 and the pixel electrode 132 constituting the dot display dot. The pixel electrode 132 is connected to the source line 134 via the TFT 133. Reference numeral 135 denotes a gate line. In this case, an oblique electric field is generated at the edge portion of the pixel formed by the pixel electrode 132 and the counter electrode 131. As a result, the aforementioned display unevenness may be a problem.

  The present invention has been made in view of these problems. That is, an object of the present invention is to improve the display performance of a VA mode liquid crystal display element. More specifically, an object of the present invention is to provide a VA mode liquid crystal display element in which display unevenness is inconspicuous and display performance with a wide display viewing angle is improved.

  Other objects and advantages of the present invention will become apparent from the following description.

According to the present invention, a pair of liquid crystal layers made of liquid crystal having negative dielectric anisotropy is provided with an electrode layer, and the liquid crystal has a pretilt angle of a predetermined angle and is aligned so as to be substantially vertically aligned. A liquid crystal cell sandwiched between
In a liquid crystal display element comprising a pair of polarizing plates sandwiched between the liquid crystal cells and arranged such that the crossing angle between the absorption axis of one polarizing plate and the absorption axis of the other polarizing plate is 90 ° ± 5 ° ,
Between the liquid crystal cell and one of the pair of polarizing plates, there is a retardation plate that has a slow axis in one direction in a plane parallel to the substrate and generates a phase difference of approximately ¼ wavelength. Arranged,
Two phase differences between the liquid crystal cell and the other of the pair of polarizing plates, each having a slow axis in one direction parallel to the substrate and having a phase difference larger than ¼ wavelength A retardation layer comprising a plurality of retardation plates including a plate is disposed,
Each of the phase difference plate and the phase difference plate constituting the phase difference layer has an optical axis arranged in a direction parallel to or perpendicular to the direction in which the pretilt angle of the liquid crystal layer is formed,
Among the retardation plates constituting the retardation plate and the retardation layer, the total retardation value of the entire retardation plate in which the optical axis is arranged in parallel with the direction of formation of the pretilt angle of the liquid crystal layer, and the liquid crystal layer The total retardation value of the entire retardation plate in which the optical axis is arranged in a direction orthogonal to the direction in which the pretilt angle is formed is substantially equal.

  In the present invention, among the retardation plates constituting the retardation layer, the total retardation value of the entire retardation plate in which the optical axis is arranged in parallel with the pretilt angle forming direction of the liquid crystal layer, and the liquid crystal layer The difference from the total retardation value of the entire retardation plate in which the optical axis is arranged in a direction perpendicular to the pretilt angle forming direction is preferably substantially equal to the quarter-wave phase difference.

  In the present invention, the retardation plate constituting the retardation layer has positive optical activity with one direction in a plane parallel to the substrate as an optical axis, and has a value larger than the retardation of a quarter wavelength. It is preferable that it consists of two phase difference plates which have the following phase difference.

  In the present invention, each of the retardation plate and the retardation plate constituting the retardation layer can be a uniaxial retardation plate.

  In the present invention, the liquid crystal display element may be a passive matrix liquid crystal display element.

  In the present invention, the liquid crystal display element may be an active matrix liquid crystal display element having an active element for each pixel.

  According to the present invention, in the VA mode liquid crystal display element, it is possible to improve the display performance so that the alignment unevenness generated when a voltage is applied is not noticeable.

Embodiment 1 FIG.
The liquid crystal display element 1 in the present embodiment is configured by sandwiching a vertically aligned liquid crystal cell in which a conventional VA mode is provided with a retardation plate for widening a viewing angle between a pair of linear polarizing plates, While sandwiching a vertical alignment type liquid crystal cell between a pair of circularly polarizing plates, the circularly polarizing plate has a retardation plate for expanding a viewing angle, that is, a retardation plate (hereinafter referred to as a retardation plate) that generates a retardation of ½ wavelength. (referred to as a λ / 2 plate). In addition, a circularly-polarizing plate shall combine a polarizing plate and a quarter wavelength phase difference plate.

  One of the pair of circularly polarizing plates sandwiching the vertical alignment type liquid crystal cell is configured by combining a linearly polarizing plate and a retardation plate that generates a phase difference of approximately ¼ wavelength. The other is integrated with one of the retardation layers for expanding the viewing angle, that is, a pair of λ / 2 plates in which the optical axes are orthogonal to each other, resulting in a quarter wavelength. A phase difference plate having a larger phase difference than the above phase difference and a linear polarizing plate are combined. The circularly polarizing plate is formed by combining a polarizing plate and a quarter wavelength retardation plate.

  The vertically aligned liquid crystal cell is sandwiched between a pair of viewing angle compensation films, for example, a uniaxial retardation plate, or the paired uniaxial retardation plates are stacked and combined, and the liquid crystal cell is disposed on the liquid crystal cell. Further, the structure is sandwiched between a pair of retardation plates that generate a phase difference of ¼ wavelength, and further, the structure is sandwiched between a pair of linear polarizers, in the present embodiment. Although it may be possible to realize viewing angle characteristics and display unevenness performance similar to those of the liquid crystal display element 1, the structure is complicated, the number of parts increases, and manufacturing becomes difficult.

  Although the liquid crystal display element 1 according to the present embodiment has a relatively simple structure, it can realize excellent viewing angle characteristics and display unevenness performance at a high level at the same time.

  In contrast to the conventional VA mode that uses a linearly polarizing plate, the liquid crystal display element 1 in the present embodiment adopts a polarizing plate configuration that has substantially circularly polarizing performance, and thus is driven by voltage application. The generated alignment unevenness becomes inconspicuous, and at the same time, it is possible to improve the display uniformity performance while realizing the widening of the viewing angle.

  FIG. 1 is a schematic configuration diagram for explaining the structure and optical specifications of the liquid crystal display element 1 in the present embodiment.

  The VA mode liquid crystal display element 1 shown in FIG. 1 is a vertical alignment type having a liquid crystal layer composed of a liquid crystal having negative dielectric anisotropy, sandwiched between a pair of substrates (not shown) whose surfaces are each subjected to vertical alignment treatment. Liquid crystal cell 2 and a pair of viewer side polarizing plates 3 (hereinafter referred to as F polarizing plates) and anti-viewer side polarizing plates 4 (hereinafter referred to as R polarized light) sandwiched between the liquid crystal cells 2 and arranged in crossed Nicols. It is called a board. Note that the crossed Nicol arrangement is an arrangement in which the crossing angle between the absorption axis of one polarizing plate and the absorption axis of the other polarizing plate is 90 ° ± 5 ° (hereinafter the same in this specification). . At this time, the liquid crystal cell is preferably monodomain aligned.

  As shown in FIG. 1, in the VA mode liquid crystal display element 1, a substrate (not shown) constituting the liquid crystal cell 2 between a polarizing plate (R polarizing plate) 4 on the non-viewer side and a vertical alignment type liquid crystal cell 2. Is provided with a retardation plate 5 (hereinafter referred to as a λ / 4 plate) having a slow axis in one direction in a plane parallel to the surface and generating a phase difference of approximately ¼ wavelength.

  Further, as shown in FIG. 1, a substrate (not shown) constituting the liquid crystal cell 2 between the viewer-side polarizing plate (F polarizing plate) 3 and the vertical alignment type liquid crystal cell 2 in the VA mode liquid crystal display element 1. ) And two retardation plates 6 and 7 having a slow axis in one direction in a plane parallel to).

  At this time, the optical axis of the phase difference plate 6 is parallel to the alignment change direction of the liquid crystal when a voltage is applied in the liquid crystal cell 2. The optical axis of the phase difference plate 7 is perpendicular to the direction of change in the orientation of the liquid crystal when a voltage is applied in the liquid crystal cell 2, and the optical axes of the phase difference plate 6 and the phase difference plate 7 are substantially orthogonal to each other. The phase difference value of the phase difference plate 7 is set larger than that of the phase difference plate 6 by the phase difference value of ¼ wavelength.

  Next, an example of a method for manufacturing the liquid crystal display element 1 will be described. In FIG. 1, the arrow shown on the F polarizing plate 3 indicates the direction of the absorption axis of the F polarizing plate 3. Similarly, the arrow shown on the R polarizing plate 4 indicates the direction of the absorption axis of the R polarizing plate 4. The liquid crystal cells 2 are sandwiched and arranged in crossed Nicols. Further, the numbers added indicate the installation angles of the absorption axes of the polarizing plates 3 and 4. In this case, the horizontal direction in the figure corresponds to the front left and right direction of the liquid crystal display element, and the counterclockwise direction is the positive direction with reference to this direction. Similarly, the arrow shown on the λ / 4 plate 5 indicates the direction of the optical axis of the λ / 4 plate.

  In FIG. 1, the solid line arrow shown in the liquid crystal cell 2 is the direction of the liquid crystal alignment treatment on the viewer side substrate holding the liquid crystal layer, and specifically, the vertical alignment provided on the substrate. The direction of rubbing performed on the film is shown. And the pretilt angle of the liquid crystal display element 1 is formed in this rubbing direction. Similarly, the arrow made of a dotted line shown in the liquid crystal cell 2 is the direction of the liquid crystal alignment treatment on the substrate on the side opposite to the viewer who sandwiches the liquid crystal layer. Specifically, the vertical alignment provided on this substrate The direction of rubbing relative to the membrane is indicated.

  The rubbing directions of the upper and lower substrates sandwiching the liquid crystal layer are antiparallel to each other. Further, the numbers added indicate the installation angle of the upper substrate in the rubbing direction. In this case, the horizontal direction in the figure corresponds to the front left and right direction of the liquid crystal display element, and the counterclockwise direction is the positive direction with reference to this direction.

  When a voltage is applied, the liquid crystal changes its orientation from a vertically aligned state having a pretilt angle formed substantially uniformly to a pretilt angle direction, that is, a direction parallel to the arrow.

  In manufacturing the liquid crystal display element 1, first, an electrode layer patterned in a stripe shape is provided on a pair of glass substrates so that a desired image can be displayed. The electrode layer can be, for example, an ITO (Indium Tin Oxide) electrode.

Next, an insulating film is provided on the glass substrate so as to cover the electrode layer. The insulating film can be, for example, a film made of SiO ₂ —TiO ₂ formed by a sol-gel method.

  Next, an alignment film is formed in the liquid crystal layer so that the liquid crystal is vertically aligned as an initial alignment state. For example, an alignment film having a thickness of about 600 mm can be formed by forming an alignment film material (trade name: JALS-2021) manufactured by JSR Corporation by flexographic printing and baking the substrate at 180 ° C. it can. Next, a rubbing process is performed on the surface of the alignment film to determine the operation direction of the liquid crystal when the electric field is applied.

  Next, a liquid crystal layer is formed by sandwiching a liquid crystal having negative dielectric anisotropy between the substrates after the alignment film forming step. At this time, for example, the distance (d) between the substrates can be kept constant by using a resin spacer. Further, as the liquid crystal layer, for example, a liquid crystal layer having a refractive index anisotropy (Δn) of 0.08918 can be used. In this case, when d = 8.3 μm, the retardation (Δn · d) of the liquid crystal display element 1 is 740 nm.

  Next, a λ / 4 plate is provided. Specifically, the surface of the liquid crystal cell 2 on the anti-viewer side is made by Sumitomo Chemical Co., Ltd. so that the optical axis provided is parallel to the direction of the liquid crystal alignment treatment on the anti-viewer side substrate holding the liquid crystal layer. A uniaxial retardation plate 5 is disposed. As a characteristic of this λ / 4 plate, the retardation value (Δn · d value) is 140 nm.

  Next, one retardation plate of the retardation layer on the viewer side surface of the liquid crystal cell 2 so that the optical axis provided is parallel to the direction of the liquid crystal alignment treatment on the viewer side substrate holding the liquid crystal layer. A uniaxial retardation plate 6 manufactured by Sumitomo Chemical Co., Ltd. is disposed. Similarly, the retardation value (Δn · d value) of the uniaxial retardation plate 6 is 550 nm.

  Next, the phase difference plate 6 is the surface on the viewer side of the liquid crystal cell 2 so that the optical axis provided forms an angle of 90 degrees with the direction of the liquid crystal alignment treatment on the viewer side substrate holding the liquid crystal layer. A uniaxial retardation plate 7 manufactured by Sumitomo Chemical Co., Ltd. is disposed as another retardation layer on the upper surface of the substrate. The retardation value (Δn · d value) of the uniaxial retardation plate 7 is 690 nm which is larger than the uniaxial retardation plate 6 of the retardation value 550 nm by a phase difference of λ / 4.

  As a result, the two-layer retardation plates 6 and 7 provided on the viewer-side surface of the liquid crystal cell 2 have optical axes orthogonal to each other and form an angle of 90 degrees with each other. The uniaxial retardation plate 7 in the upper layer has a larger retardation value, and each difference is substantially equal to the phase difference of λ / 4.

  Next, the polarizing plates 3 and 4 are installed. Specifically, the liquid crystal cell 2 provided with the two-layer retardation plates 6 and 7 is sandwiched, and the polarizing plates 3 and 4 are pasted so as to have a crossed Nicols arrangement.

  As shown in FIG. 1, the structure and optical specifications of the liquid crystal display element are set so that the absorption axis of the uppermost F-polarizing plate 3 has an angle of 45 degrees from the direction indicated by the arrow in FIG. It is. As a result, the absorption axis of the F polarizing plate 3 forms an angle of 45 degrees with the optical axis of the adjacent retardation plate 7, and the absorption axis of the R polarizing plate 4 has an angle of 45 degrees with the optical axis of the adjacent λ / 4 plate 5. The angle will be made.

  The liquid crystal cell 2 is of the above-described vertical alignment type, and the liquid crystal cell determined by the rubbing direction indicated by the arrow in FIG. 1 (normally the arrow is the rubbing direction of the F-side base and the dotted arrow is the rubbing direction of the R-side base). The direction of the pretilt angle, that is, the direction of tilting operation by applying a voltage is the direction indicated by each arrow, that is, the direction that forms an angle of 270 degrees from the horizontal direction in the figure.

  Although not shown in detail, the liquid crystal display element 1 in the present embodiment has a passive matrix structure. That is, each pixel portion constituting the image display is not provided with a switching element such as a TFT, and a target image is displayed by passive driving using an electrode layer.

  Next, when the liquid crystal display element 1 according to the present embodiment was used to perform image display by passive driving by 1/4 duty driving, display with a wide viewing angle without display unevenness was realized.

  Next, as a comparative example, a conventional VA mode liquid crystal display element 20 with a wide viewing angle was produced.

  FIG. 2 is a schematic configuration diagram for explaining the structure and optical specifications of a liquid crystal display element 20 which is a comparative example of the present embodiment.

  The VA mode liquid crystal display element 20 shown in FIG. 2 is a vertical alignment type having a liquid crystal layer composed of a liquid crystal having negative dielectric anisotropy, sandwiched between a pair of substrates (not shown) whose surfaces are each subjected to vertical alignment treatment. Liquid crystal cell 22 and a pair of viewer side polarizing plates 23 (hereinafter referred to as F polarizing plates) and anti-viewer side polarizing plates 4 (hereinafter referred to as R polarized light) sandwiched between the liquid crystal cells 22 and arranged in crossed Nicols. It is called a board. At this time, the liquid crystal cell has a monodomain alignment.

  In addition, the manufacturing method of the liquid crystal cell 22 was the same as that of the liquid crystal cell 2 which comprises the liquid crystal display element 1 of this embodiment mentioned above.

  As shown in FIG. 2, in the VA mode liquid crystal display element 20, a substrate (not shown) constituting the liquid crystal cell 22 is provided between the viewer-side polarizing plate (R polarizing plate) 23 and the vertical alignment type liquid crystal cell 22. A pair of λ / 2 plates 26 and 27 having a slow axis in one direction in a parallel plane are stacked. The λ / 2 plates 26 and 27 are manufactured by Sumitomo Chemical Co., Ltd., and are uniaxial retardation plates having the same retardation value of 550 nm.

  The optical axis of the λ / 2 plate 26 is parallel to the alignment change direction of the liquid crystal when a voltage is applied in the liquid crystal cell 22. The optical axis of the λ / 2 plate 27 is perpendicular to the direction of change in the orientation of the liquid crystal when a voltage is applied in the liquid crystal cell 22, and the optical axes of the λ / 2 plate 26 and the λ / 2 plate 27 are substantially the same. Orthogonal.

  In FIG. 2, the arrow shown on the F polarizing plate 23 indicates the direction of the absorption axis of the F polarizing plate 23. Similarly, the arrow shown on the R polarizing plate 24 indicates the direction of the absorption axis of the R polarizing plate 24. The liquid crystal cells 22 are sandwiched and arranged in crossed Nicols. Further, the numbers added indicate the installation angles of the absorption axes of the polarizing plates 23 and 24. In this case, the horizontal direction in the figure corresponds to the front left and right direction of the liquid crystal display element, and the counterclockwise direction is the positive direction with reference to this direction. Similarly, the arrows shown on the λ / 2 plates 26 and 27 indicate the directions of the optical axes of the λ / 2 plates 26 and 27.

  In FIG. 2, the solid arrow shown in the liquid crystal cell 22 is the direction of the liquid crystal alignment treatment on the viewer side substrate holding the liquid crystal layer. Specifically, the vertical alignment provided on this substrate The direction of rubbing performed on the film is shown. And the pretilt angle of the liquid crystal display element 20 is formed in this rubbing direction. Similarly, the arrow made of a dotted line shown in the liquid crystal cell 22 is the direction of the liquid crystal alignment treatment on the substrate on the side opposite to the viewer who holds the liquid crystal layer, and specifically, the vertical alignment provided on the substrate. The direction of rubbing relative to the membrane is indicated. The rubbing directions of the upper and lower substrates sandwiching the liquid crystal layer are antiparallel to each other. Further, the numbers added indicate the installation angle of the upper substrate in the rubbing direction. In this case, the horizontal direction in the figure corresponds to the front left and right direction of the liquid crystal display element, and the counterclockwise direction is the positive direction with reference to this direction.

  When a voltage is applied, the liquid crystal changes its orientation from a vertically aligned state having a pretilt angle formed substantially uniformly to a pretilt angle direction, that is, a direction parallel to the arrow.

  Next, the display performance was compared using the liquid crystal display element 1 and the comparative example 20 in the present embodiment having the above-described configuration. As for the driving of each element 1, 20, passive driving by 1/4 duty driving with a rectangular wave (voltage 2.6 Vrms) with a frequency of 70 Hz is performed so that display unevenness is emphasized and the difference in display performance becomes clearer. The display performance was evaluated by visual comparison. As a result, the viewing angle characteristics of the images displayed on each of the display elements 1 and 20 were substantially the same and both were good.

  Next, each display unevenness characteristic was compared and evaluated. In the liquid crystal display element 20 as a comparative example, severe display unevenness caused by an alignment shift caused by an oblique electric field was visually recognized in the peripheral portion of each display pixel. On the other hand, in the liquid crystal display element 1 according to the present embodiment, display unevenness is not confirmed in the entire pixel portion including the peripheral portion of each display pixel, and display performance with significantly improved display uniformity is realized. I understood.

  From the above, it was found that the liquid crystal display element 1 according to the present embodiment can achieve both a wide viewing angle and a reduction in display unevenness, that is, an improvement in display uniformity.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, the liquid crystal display element 1 in the present embodiment is a passive matrix type VA mode liquid crystal display element, but the present invention is not limited to this. As the liquid crystal cell, a liquid crystal cell having the same structure as the active matrix liquid crystal cell 130 shown in FIG. 5 is used, and the other configuration is the same as that of the liquid crystal display element 1, thereby wide viewing angle characteristics and excellent display uniformity. Thus, an active matrix type VA mode liquid crystal display element having both compatibility can be obtained.

  As described above, according to the present invention, it is possible to provide a liquid crystal display element excellent in display quality and appearance. Further, this liquid crystal display element is excellent in that the ON brightness is improved by eliminating black display unevenness, and that the response speed of the liquid crystal is improved by applying a high voltage by reducing the display unevenness. Display performance can be realized.

It is a typical block diagram for demonstrating the structure and optical specification of the liquid crystal display element in this Embodiment. It is a typical block diagram for demonstrating the structure and optical specification of the liquid crystal display element which are the comparative examples of this Embodiment. It is a cross-sectional view of a VA mode liquid crystal cell. It is explanatory drawing of the generation | occurrence | production mechanism of the display nonuniformity in a VA mode liquid crystal display element. It is a typical principal part top view of a passive matrix type VA mode liquid crystal display element. It is a typical principal part top view of a passive matrix type conventional VA mode liquid crystal display element. It is a typical principal part top view of an active matrix type VA mode liquid crystal display element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20 Liquid crystal display element 2,22 Liquid crystal cell 3,4,23,24 Polarizing plate 5 (lambda) / 4 board 6,7,26,27 Phase difference plate 100 Liquid crystal cell 101 Liquid crystal layer 102,103 Electrode 104 Vertical electric field 105 Diagonal Electric field 106 Pretilt angle forming direction 107 Oblique electric field Heisei direction 110, 120, 130 VA mode liquid crystal display element 111, 121 Segment electrode 112, 122 Common electrode 123, 124 Electrode wiring 131 Counter electrode 132 Pixel electrode 133 TFT
134 Source line

Claims (6)

A liquid crystal layer composed of a liquid crystal having negative dielectric anisotropy is sandwiched between a pair of substrates having an electrode layer and aligned so that the liquid crystal has a pretilt angle of a predetermined angle and is substantially vertically aligned. A liquid crystal cell,
In a liquid crystal display element comprising a pair of polarizing plates sandwiched between the liquid crystal cells and arranged such that the crossing angle between the absorption axis of one polarizing plate and the absorption axis of the other polarizing plate is 90 ° ± 5 ° ,
Between the liquid crystal cell and one of the pair of polarizing plates, there is a retardation plate that has a slow axis in one direction in a plane parallel to the substrate and generates a phase difference of approximately ¼ wavelength. Arranged,
Two phase differences between the liquid crystal cell and the other of the pair of polarizing plates, each having a slow axis in one direction parallel to the substrate and having a phase difference larger than ¼ wavelength A retardation layer comprising a plurality of retardation plates including a plate is disposed,
Each of the phase difference plate and the phase difference plate constituting the phase difference layer has an optical axis arranged in a direction parallel to or perpendicular to the direction in which the pretilt angle of the liquid crystal layer is formed,
Among the retardation plates constituting the retardation plate and the retardation layer, the total retardation value of the entire retardation plate in which the optical axis is arranged in parallel with the direction of formation of the pretilt angle of the liquid crystal layer, and the liquid crystal layer A liquid crystal display element characterized in that the total retardation value of the entire retardation plate in which the optical axis is arranged in a direction orthogonal to the pretilt angle forming direction is substantially equal.   Among the retardation plates constituting the retardation layer, the total retardation value of the entire retardation plate in which the optical axis is arranged in parallel with the formation direction of the pretilt angle of the liquid crystal layer, and the formation of the pretilt angle of the liquid crystal layer 2. The liquid crystal according to claim 1, wherein a difference from a total retardation value of the entire retardation plate in which the optical axis is arranged in a direction orthogonal to the direction is substantially equal to a quarter-wave phase difference. Display element.   The retardation plate constituting the retardation layer has two retardations having a slow axis in one direction in a plane parallel to the substrate and a value larger than a quarter wavelength retardation. The liquid crystal display element according to claim 1, comprising a retardation plate.   4. The liquid crystal display element according to claim 1, wherein each of the retardation plate and the retardation plate constituting the retardation layer is a uniaxial retardation plate. 5.   The liquid crystal display element according to claim 1, wherein the liquid crystal display element is a passive matrix type liquid crystal display element.   The liquid crystal display element according to claim 1, wherein the liquid crystal display element is an active matrix type liquid crystal display element having an active element for each pixel.

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