JP2008158426A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a VA mode liquid crystal display element with display unevenness due to a rubbing flaw improved. <P>SOLUTION: The VA mode liquid crystal display element 1 is such that the liquid crystal of a liquid crystal layer, having negative dielectric anisotropy contains a chiral agent and also has a twist angle of 90±5° between a pair of substrates between which the liquid crystal is sandwiched. Those substrates have alignment layers, having vertical alignment property by being rubbed. Angles between the axes of absorption of polarizers 3 and 4 and directions of rubbing processing of the substrates adjacent to the polarizers 3 and 4 are both set to 0 to 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. As a result, the product (Δn · d) of the refractive index anisotropy (Δn) of the liquid crystal and the liquid crystal layer thickness (d) equal to the distance between the pair of substrates in the portion where the voltage is applied and the portion where the voltage is not applied. ) Depending on the light transmission characteristics, particularly the color. By utilizing this difference, a desired display can be performed.

JP-A-3-215830 JP-A-9-325339

  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.

  In the VA mode, as described above, the liquid crystal layer is not initially completely aligned when no voltage is applied, but is devised so that the alignment is substantially vertical. When the initial alignment of the liquid crystal layer is a complete vertical alignment, the direction of the tilting operation of the liquid crystal when a voltage is applied is not determined, and a situation occurs in which regions tilted in different directions in the plane of the liquid crystal cell are mixed. This situation is recognized by the viewer as a so-called domain, and results in a significant deterioration in the display quality of the liquid crystal display element.

  Therefore, the liquid crystal layer is often in an alignment state that has a pretilt angle of a predetermined angle from the normal direction that is the thickness direction of the liquid crystal layer and has a substantially uniform vertical alignment. Thereby, when a voltage is applied, the direction of the tilting operation of the liquid crystal can be determined in one desired direction. As a result, the uniformity in the display surface of the liquid crystal display element is maintained, so that the high display quality inherent in the VA mode can be realized at a high level.

  Here, as a method for forming a state in which the liquid crystal layer has a pretilt angle of a predetermined angle and is vertically aligned substantially uniformly, a vertical alignment layer, for example, a vertical alignment liquid crystal alignment film (hereinafter referred to as alignment film) is used. And an alignment treatment method using a rubbing treatment in combination.

  Specifically, in a VA mode liquid crystal cell, first, a vertical alignment film is provided on the surface of the substrate sandwiching the liquid crystal layer, and then the surface of the alignment film is rubbed in the direction of the desired liquid crystal tilting operation. Process. Thereby, said orientation state is realizable.

  By the way, in the VA mode, there may be a problem in display uniformity due to the application of the rubbing process. The rubbing treatment is performed, for example, by covering the surface of a metal cylindrical rubbing roll having a predetermined diameter with a rubbing cloth made of velvet, and rubbing the surface of the alignment film with the rubbing cloth while rotating the rubbing cloth at a high speed. At this time, the forming direction and the size of the pretilt angle of the liquid crystal layer are determined by the strength and direction of rubbing the surface of the alignment film with the rubbing cloth. That is, in the rubbing process, the initial alignment state of the liquid crystal layer, that is, the formation state of the pretilt angle is controlled by the rubbing intensity and direction.

  However, since the cloth is used in the rubbing treatment, a problem at a level caused by each hair constituting the cloth may occur. In other words, by rotating a metal roll whose surface is covered with a rubbing cloth at high speed, it is possible to perform almost uniform processing on a macro scale, but when viewed at a micro level, it achieves perfect uniformity. It is difficult. That is, for each of the hairs that make up the rubbing cloth, the characteristics are slightly different, and there is a difference in how the force is applied, so the rubbing strength and rubbing direction when rubbing the alignment film are different. It will be uneven. As a result, a so-called rubbing scratch problem may occur in the VA mode due to such fine variations.

  The rubbing scratches are generated due to fine variations in the rubbing strength during the rubbing process. When the rubbing scratch exceeds a certain level, it is recognized as a scratch or display unevenness by the viewer in the state of the liquid crystal display device.

  At the location where the rubbing scratch has occurred, the magnitude of the pretilt angle of the liquid crystal layer differs from the normal region, and there is also a deviation in the pretilt angle forming direction. Here, the shift in the pretilt angle forming direction is a shift in the azimuth angle in the in-plane direction of the substrate in the initial alignment state of the liquid crystal. Among these, the main factor of scratches and display unevenness is the difference in the pretilt angle of the liquid crystal layer.

  When an abnormal region having a different pretilt angle occurs in the liquid crystal layer, a difference occurs between the phase difference in the thickness direction of the liquid crystal layer in the region and the phase difference in other normal regions. And since this difference appears as a difference in transmittance when no voltage is applied, it is recognized as a scratch or display unevenness.

  FIG. 5 is a schematic configuration diagram for explaining the structure and optical specifications of a conventional VA mode. In the VA mode 100, as shown in FIG. 5, a liquid crystal layer (not shown) made of liquid crystal having negative dielectric anisotropy is sandwiched between a pair of substrates (not shown) whose surfaces are each vertically aligned. Thus, the liquid crystal cell 101 is configured. The liquid crystal cell 101 is sandwiched between a pair of polarizing plates 102 and 103 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 °. Thus, a liquid crystal display element is configured. Thereby, when no voltage is applied, black display that is OFF display due to the initial vertical alignment is realized. When the liquid crystal layer in the liquid crystal cell 101 is tilted by applying a voltage, light is transmitted between the pair of polarizing plates 102 and 103 sandwiching the liquid crystal cell 101, and ON display is realized.

  In FIG. 5, the arrow shown on the polarizing plate 102 indicates the direction of the absorption axis of the polarizing plate 102. Similarly, the arrow shown on the polarizing plate 103 indicates the direction of the absorption axis of the polarizing plate 103. The liquid crystal cells 101 are sandwiched and arranged in crossed Nicols. 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). . Further, the numbers added indicate the installation angles of the absorption axes of the polarizing plates 102 and 103. 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.

  Also, in FIG. 5, the solid arrow shown in the liquid crystal cell 101 is the direction of the liquid crystal alignment treatment on the viewer side substrate sandwiching the liquid crystal layer. Specifically, the arrow is provided on this substrate. The direction of the rubbing process performed on the vertical alignment film is shown. A pretilt angle of the VA mode 100 is formed in the rubbing direction. Similarly, the dotted arrow shown in the liquid crystal cell 101 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. Specifically, the vertical alignment provided on the substrate The direction of the rubbing process with respect to a film | membrane is shown.

  The rubbing treatment directions of the upper and lower substrates sandwiching the liquid crystal layer are antiparallel to each other. Further, the numerals added indicate the installation angle in the direction of the rubbing process of the upper substrate. 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.

  In the VA mode 100, the direction of the rubbing treatment of the substrate constituting the liquid crystal cell 101 is approximately 45 ° with respect to the absorption axes of the polarizing plates 102 and 103, respectively. This configuration is OFF when there is a variation in the phase difference in the plane of the liquid crystal cell due to the variation in the rubbing strength in the rubbing process, especially when there is a minute region where the rubbing strength is stronger than the others and the phase difference is slightly larger. It has a configuration that easily acts as a cause of light leakage display failure during display. For this reason, in the conventional VA mode, a slight variation in the phase difference in the display surface resulting from the rubbing process also causes display defects.

  As described above, in the conventional VA mode, display defects due to rubbing scratches are likely to occur, and it is difficult to ensure display uniformity. Therefore, display unevenness sometimes becomes a problem.

  The present invention has been made in view of these problems. That is, an object of the present invention is to improve display performance in 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 not noticeable and the display viewing angle is wide.

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

The present invention provides a liquid crystal layer in which a liquid crystal layer composed of a liquid crystal having negative dielectric anisotropy is sandwiched between a pair of substrates that have been aligned so that the liquid crystal has a predetermined pretilt angle and is substantially vertically aligned Cell,
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 ° In
The liquid crystal is a chiral nematic liquid crystal containing a chiral agent and having a twist angle of 90 ° ± 5 ° between the substrates to constitute the liquid crystal layer,
The alignment treatment is a rubbing treatment for an alignment layer formed on the surface of the substrate,
The angle formed by one absorption axis of the polarizing plate and the rubbing direction in one of the substrates adjacent to the polarizing plate, and the other absorption axis of the polarizing plate and the substrate adjacent to the polarizing plate The angle formed with the direction of the rubbing process on the other side is 0 ° or more and 7 ° or less.

  In the present invention, an angle formed by one absorption axis of the polarizing plate and a rubbing treatment direction in one of the substrates adjacent to the polarizing plate, and the other absorption axis of the polarizing plate, It is preferable that the angle between the other of the adjacent substrates and the direction of the rubbing treatment is 0 degree or more and 3 degrees or less.

In the present invention, 0 <d / p ≦ 0.4 between the natural twist pitch p of the liquid crystal and the distance d between the substrates.
It is preferable that the relationship is established.

In the present invention, 0 <d / p ≦ 0.2 between the natural twist pitch p of the liquid crystal and the distance d between the substrates.
It is more preferable that the relationship is established.

  In the present invention, it is preferable that at least one retardation film having a negative retardation value in the thickness direction of the liquid crystal cell is provided between at least one of the polarizing plates and the liquid crystal cell.

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

  According to the present invention, in the VA mode liquid crystal display element, it is possible to improve display performance so that rubbing scratches found when no voltage is applied are not noticeable.

Embodiment 1 FIG.
The liquid crystal display element 1 in the present embodiment is configured by sandwiching a substantially vertical alignment type liquid crystal cell in which the rubbing directions of the upper and lower substrates in which the VA mode sandwiches the liquid crystal layer is antiparallel to each other, with a pair of linear polarizing plates. On the other hand, a 90 ° twisted substantially vertical alignment type liquid crystal cell having a structure in which the liquid crystal layer is twisted by 90 ° between the upper and lower substrates sandwiching the liquid crystal layer is sandwiched between a pair of linear polarizing plates.

The absorption axis of one polarizing plate of the pair of polarizing plates sandwiching the substantially vertical alignment type liquid crystal cell, the direction of rubbing treatment in one of the pair of substrates adjacent to the polarizing plate, and the other The polarizing plate and the rubbing treatment direction on one of the pair of substrates adjacent to the polarizing plate are both substantially parallel directions.
Although the liquid crystal display element 1 according to the present embodiment has a relatively simple structure, it can simultaneously realize excellent viewing angle characteristics and display unevenness resistance due to rubbing scratches at a high level.

  That is, in the liquid crystal display element 1 according to the present embodiment, the absorption axis of the polarizing plate that sandwiches the liquid crystal cell and the rubbing direction of the adjacent substrates of the pair of substrates constituting the liquid crystal cell are substantially parallel directions. Unlike the conventional VA mode, each of which is approximately 45 ° from each other, the rubbing scratch display unevenness in the direction matching the rubbing direction becomes inconspicuous, and at the same time, the viewing angle is enlarged and the display uniformity performance is improved. Is possible.

  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.

  A VA mode liquid crystal display element 1 shown in FIG. 1 is composed of a chiral nematic liquid crystal that is sandwiched between a pair of substrates (not shown) whose surfaces are each subjected to vertical alignment treatment and contains a chiral agent and has negative dielectric anisotropy. A vertically aligned liquid crystal cell 2 having a liquid crystal layer, a pair of viewer side polarizing plates 3 (hereinafter referred to as F polarizing plates) and a counter viewer side sandwiched between the liquid crystal cells 2 and arranged in crossed Nicols. A polarizing plate 4 (hereinafter referred to as an R polarizing plate). As described above, the crossed Nicol arrangement means 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 °. At this time, the liquid crystal cell is preferably monodomain aligned.

  The liquid crystal cell 2 has a 90 ° twisted substantially vertical alignment type structure in which the liquid crystal layer is twisted by 90 ° between the upper and lower substrates sandwiching the liquid crystal layer. The absorption axis of the F-polarizing plate 3 sandwiching the liquid crystal cell 2 and the rubbing treatment direction on the adjacent upper substrate of the pair of substrates constituting the liquid crystal cell are parallel to each other. And the rubbing treatment direction on the adjacent lower substrate of the pair of substrates constituting the liquid crystal cell 2 are parallel to each other.

  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.

  Further, in FIG. 1, the solid arrow shown in the liquid crystal cell 2 is the direction of the liquid crystal alignment treatment on the viewer-side upper substrate sandwiching the liquid crystal layer. Specifically, the arrow is provided on this substrate. The direction of rubbing performed on the vertical alignment film is shown. And the pretilt angle of the liquid crystal display element 1 is formed in this rubbing direction. Similarly, the dotted arrow shown in the liquid crystal cell 2 is the direction of the liquid crystal alignment treatment on the lower substrate on the side opposite to the viewer who sandwiches the liquid crystal layer. Specifically, the arrow is provided on this substrate. The direction of rubbing with respect to the vertical alignment film is shown. The rubbing directions of the upper and lower substrates sandwiching the liquid crystal layer are set to make an angle of 90 ° with each other.

  When a voltage is applied, the liquid crystal forms a surface constituting the liquid crystal cell 2 in accordance with the pretilt angle forming direction from a substantially vertical alignment state having a twist angle of 90 ° formed substantially uniformly with a pretilt angle. Tilt in a direction parallel to

  The production of the liquid crystal display element 1 will be described. In the manufacturing method, 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, using a pair of substrates that have gone through the alignment film formation process, the rubbing direction of each other is set to be 90 °, and a chiral agent is included so that a twisted structure can be introduced into the liquid crystal layer. A liquid crystal layer is formed by sandwiching a liquid crystal having negative dielectric anisotropy. 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 = 6.0 μm, the retardation (Δn · d) of the liquid crystal display element 1 is 535 nm.

  Specifically, d / p = 0 so that the natural twist pitch p of the liquid crystal and the distance d between the pair of substrates constituting the liquid crystal cell 2 have a relationship of 0 <d / p ≦ 0.2. The amount of the chiral agent contained in the liquid crystal is adjusted so as to be 0.01.

  Next, the polarizing plates 3 and 4 are installed. Specifically, a pair of predetermined-shaped polarizing plates NPF-SEG-1425DU made by Nitto Denko Corporation are used, and the liquid crystal cell 2 is sandwiched and pasted so that the polarizing plates 3 and 4 are in a crossed Nicol arrangement. .

  As shown in FIG. 1, the structure and optical specifications of the liquid crystal display element 1 are such 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. Set. Then, the absorption axis of the F-polarizing plate 3 is parallel to the rubbing process direction of the adjacent upper substrate among the substrates constituting the liquid crystal cell, and the angle between them is 0 degree. Similarly, the absorption axis of the R polarizing plate 4 is parallel to the rubbing processing direction of the lower substrate of the adjacent liquid crystal cell, and the angle between them is 0 degree.

  The liquid crystal cell 2 is the vertical alignment type described above. The direction of the pretilt angle of the liquid crystal determined by the rubbing direction indicated by the straight arrows in FIG. 1 (normal arrow is the rubbing direction of the F-side substrate; dotted arrow is the rubbing direction of the R-side substrate), that is, voltage application The direction of tilting operation is the direction indicated by each arrow. A curved arrow connecting two straight arrows shown in the liquid crystal cell 2 of FIG. 1 indicates that the liquid crystal layer of the liquid crystal cell 2 has a twist structure. The twist angle at this time can be 90 °.

  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, the liquid crystal display element which is the 1st comparative example of this Embodiment was manufactured. The structure and optical specifications are the same as those of the conventional VA mode 100 shown in FIG. Therefore, for convenience, the same reference numerals are used for corresponding configurations. And about a more specific structure, the liquid crystal which comprises the liquid crystal cell 101 is a thing mentioned above except that the refractive index anisotropy ((DELTA) n) by Merck Co., Ltd. which does not contain a chiral agent is 0.08918. The manufacturing method and materials used are the same as those of the liquid crystal display element 1 in the embodiment.

  Using the thus-obtained liquid crystal display element 1 in the present embodiment and the liquid crystal display element 100 as the first comparative example, an enlarged observation comparative evaluation is performed by using a microscope for the occurrence of rubbing scratch display failure when the voltage is OFF. It was. As a result, in the first comparative example 101 which is the conventional VA mode, rubbing scratches are conspicuous and a rubbing scratch display defect occurs, whereas in the liquid crystal display element 1 in the present embodiment, rubbing scratches are hardly confirmed, and rubbing scratches are observed. It was found that there was no display defect. Therefore, according to the liquid crystal display element 1 in the present embodiment, it has been found that rubbing scratches do not occur or are slight even if they occur, and display defects due to rubbing scratches are not visually recognized.

  Next, a liquid crystal display element 20 as a second comparative example of the present embodiment was manufactured.

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

  In the liquid crystal display element 20, as shown in FIG. 2, a liquid crystal layer (not shown) made of liquid crystal having negative dielectric anisotropy is sandwiched between a pair of substrates (not shown) whose surfaces are each subjected to vertical alignment treatment. Thus, a liquid crystal cell 21 is formed, and the liquid crystal cell 21 is composed of 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 °. A liquid crystal display element is formed by being sandwiched between the plates 22 and 23. Therefore, when no voltage is applied, black display, which is OFF display derived from the initial vertical alignment, is realized.

  In FIG. 2, the arrow shown on the polarizing plate 22 indicates the direction of the absorption axis of the polarizing plate 22. Similarly, the arrow shown on the polarizing plate 23 indicates the direction of the absorption axis of the polarizing plate 23. The liquid crystal cells 21 are sandwiched and arranged in crossed Nicols. Further, the numbers added indicate the installation angles of the absorption axes of the polarizing plates 22 and 23. 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.

  Further, in FIG. 1, the solid arrows shown in the liquid crystal cell 21 indicate the direction of liquid crystal alignment treatment on the viewer side substrate sandwiching the liquid crystal layer, and specifically, provided on this substrate. The direction of the rubbing process performed on the vertical alignment 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 21 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. Specifically, the vertical alignment provided on this substrate The direction of the rubbing process with respect to a film | membrane is shown. The directions of rubbing treatment of the upper and lower substrates that sandwich the liquid crystal layer are antiparallel to each other.

  As described above, in the liquid crystal display element 20 as the comparative example, the rubbing treatment direction of the pair of substrates constituting the liquid crystal cell 21 is on the viewer side with respect to the absorption axes of the polarizing plates 22 and 23 provided. The substrate is in the parallel direction, and the lower substrate on the non-viewer side is in the direction of 90 °.

  In addition, about the material used for the liquid crystal display element 20, and the manufacturing method of the liquid crystal display element 20, the liquid crystal which comprises the liquid crystal cell 21 does not contain a chiral agent, and the refractive index anisotropy ((DELTA) n) by Merck Ltd. is 0. 0.08918 is the same as the liquid crystal display element 1 in the present embodiment described above except that it is 0.00818.

  Using the liquid crystal display element 1 according to the present embodiment and the liquid crystal display element 21 which is the second comparative example, a magnified observation comparative evaluation with a microscope was performed on the occurrence of rubbing scratch display failure when the voltage was OFF. As a result, it was found that the rubbing scratches were conspicuous and the rubbing scratch display defect occurred in the liquid crystal display element 21 as the second comparative example, compared to the liquid crystal display element 1 in the present embodiment.

  Next, static driving is performed by applying a rectangular wave having a voltage of 2.5 V and a frequency of 70 Hz using the liquid crystal display element 1 according to the present embodiment and the liquid crystal display element 21 which is the second comparative example. The transmittance of each liquid crystal display element when performing bright display as display was evaluated and compared. As a result, in the liquid crystal display element 1 according to the present embodiment, a high transmittance of 6.7% is achieved at the time of ON display and a clear bright display is realized, whereas the liquid crystal display which is the second comparative example In the element 21, the transmittance during ON display was 0.1%, and it was confirmed that clear bright display could not be achieved. Therefore, it can be seen that the optical specification of the liquid crystal display element 21 as the second comparative example cannot provide a liquid crystal display element showing a sufficient contrast ratio.

  In the liquid crystal display element according to the present embodiment, at least one phase difference having a negative retardation value in the thickness direction of the liquid crystal cell 2 between at least one of the pair of polarizing plates 3 and 4 and the liquid crystal cell 2. It is also possible to have a film. By adopting such a configuration, the liquid crystal display element in this embodiment can realize more excellent viewing angle characteristics.

Embodiment 2. FIG.
In this embodiment mode, a preferable range of an angle between the absorption axis of the polarizing plate and the direction of rubbing treatment on the substrate constituting the liquid crystal cell in the liquid crystal display element of Embodiment Mode 1 will be described.

  First, the liquid crystal display element 1 described above except that the refractive index anisotropy (Δn) of the liquid crystal used in the liquid crystal cell is 0.1363 and the retardation (Δn · d) of the liquid crystal display element is 818 nm. A liquid crystal display element having exactly the same structure is prepared.

  Next, the arrangement of the pair of upper and lower polarizing plates remains in the crossed Nicols arrangement, and the absorption axis of the F polarizing plate is between the rubbing treatment direction of the adjacent upper substrate among the substrates constituting the liquid crystal cell and each other. The angle formed, that is, the deviation angle is 1 degree. Similarly, the absorption axis of the R polarizing plate is 1 degree where the angle formed between the rubbing treatment direction of the lower substrate of the adjacent liquid crystal cell and the mutual is the same value. A liquid crystal display element having the same structure as that of the liquid crystal display cell is prepared except that there is a certain number.

  Next, the angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the adjacent substrate, that is, the deviation angle is 2 degrees, 3 degrees, 4 degrees, 5 degrees, 6 degrees, 7 degrees, 8 degrees, 9 degrees, Nine types of liquid crystal display elements having the same structure as that of the liquid crystal display element are prepared except that the values are different from 10 degrees.

  As described above, 11 types of liquid crystal display elements having exactly the same structure were prepared except that the angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the substrate was different from 0 to 10 degrees. Was evaluated.

Specifically, a plurality of rubbing scratch areas found in each liquid crystal display element during OFF display are confirmed using a microscope, the transmittance of each area is measured to obtain an average value, and this value is determined as the transmittance of the scratch area. And Next, the transmittance of the normal region is measured for the same liquid crystal display element. And the calculation formula: CR = (transmittance of scratch area) / (transmittance of normal area)
Accordingly, a CR (contrast) value, which is a transmittance ratio between the scratch area and the normal area, is calculated. This result and the evaluation result of rubbing scratches by visual inspection were combined to obtain an acceptable CR value level.

  As a result of the evaluation, it was found that when the CR value is larger than 10, rubbing scratches may be visually confirmed by a viewer, and there is a concern about display failure. On the other hand, when the CR value was 3 or less, rubbing scratches were hardly observed, and it was found that there was almost no possibility of causing a problem as a display defect.

  Next, the relationship between the deviation angle and the CR value in each liquid crystal display element was examined.

  FIG. 3 is a diagram in which the CR values obtained with respect to the shift angle in the liquid crystal display element in the present embodiment are plotted. In FIG. 3, each plot of the evaluation results is connected by a straight line so that the graph becomes more useful.

  From the evaluation results shown in FIG. 3, it can be seen that the CR value becomes larger than 10 when the deviation angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the substrate becomes larger than 7 degrees. It can also be seen that the CR value is 3 or less when the deviation angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the substrate is 3 degrees or less.

  To summarize the above, when the deviation angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the substrate is larger than 7 degrees, the rubbing scratch may be visually confirmed by the viewer, and there is a concern that display defects may occur. On the other hand, when the deviation angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the substrate is 3 degrees or less, rubbing scratches are hardly observed, and there is almost no possibility of causing a problem as a display defect. Therefore, the deviation angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the substrate is preferably 0 degree or more and 7 degrees or less from the viewpoint of reducing the occurrence of rubbing scratches. Further, it is more preferable that the deviation angle between the absorption axis of the polarizing plate and the rubbing treatment direction of the substrate is 0 degree or more and 3 degrees or less because there is almost no occurrence of rubbing scratches and the possibility of causing a display defect is reduced. .

Embodiment 3 FIG.
In the present embodiment, in the liquid crystal display element of the first embodiment, the relationship between the natural twist pitch p of the liquid crystal in consideration of the natural twist characteristic of the liquid crystal and the distance d between the upper and lower substrates constituting the liquid crystal cell (d / A preferred range of the p value will be described.

  First, the liquid crystal display element 1 described above except that the refractive index anisotropy (Δn) of the liquid crystal used in the liquid crystal cell is 0.1363 and the retardation (Δn · d) of the liquid crystal display element is 818 nm. A liquid crystal display element having exactly the same structure is prepared. At this time, the d / p value of the liquid crystal of the liquid crystal layer constituting the liquid crystal cell is 0.01 as described above.

  Next, only the amount of the chiral agent contained in the liquid crystal of the liquid crystal layer constituting the liquid crystal cell is different, and as a result, the liquid crystal display having the same structure as the liquid crystal display cell except that the d / p value is 0.02. Prepare the device.

  Next, only the amount of chiral agent contained in the liquid crystal of the liquid crystal layer constituting the liquid crystal cell is different, and as a result, the d / p values are 0.05, 0.1, 0.2, 0.3, 0.4 , 0.5, and 0.65, except that the values are different from each other. Seven types of liquid crystal display elements having the same structure as the liquid crystal display elements are prepared.

  Finally, a liquid crystal display element having the same structure as the liquid crystal display cell is prepared except that the liquid crystal of the liquid crystal layer constituting the liquid crystal cell does not contain a chiral agent and, as a result, the d / p value is 0.

  As described above, the relationship between the natural twist pitch p of the liquid crystal and the distance d between the upper and lower substrates constituting the liquid crystal cell (d / p value) is exactly the same except that it is different in the range of 0 to 0.65. Ten types of liquid crystal display elements having the structure were prepared.

  In the evaluation, the ten types of liquid crystal display elements were subjected to time division driving with a frequency of 70 Hz, a duty ratio of 1 / 32D, and a bias ratio of 1 / 6B, and the maximum contrast ratio (maximum CR) was calculated and compared.

  Next, the relationship between the d / p value and the maximum CR in each of the above liquid crystal display elements was examined.

  FIG. 4 is a diagram in which the maximum CR value obtained with respect to the d / p value of the liquid crystal display element in the present embodiment is plotted. In FIG. 4, each plot of the evaluation results is connected by a straight line so that the graph is more useful.

  From the evaluation results shown in FIG. 4, when the relationship (d / p value) between the natural twist pitch p of the liquid crystal and the distance d between the upper and lower substrates constituting the liquid crystal cell is 0.2 or less, the maximum CR value is obtained. It can be seen that becomes a value close to or exceeding 200. It can also be seen that when the d / p value is 0.6 or less, the value of the maximum CR is close to 100 or exceeds it.

  As described above, when the d / p value is 0.6 or less, high contrast characteristics are realized in the liquid crystal display element, and it becomes possible to provide a liquid crystal display element with excellent display performance. Further, when the d / p value is 0.2 or less, a very high contrast characteristic is realized in the liquid crystal display element, and it becomes possible to provide a liquid crystal display element with very excellent display performance. Therefore, the d / p value is preferably 0 or more and 0.6 or less, and more preferably 0.2 or less.

  In the above evaluation of the display performance, the liquid crystal of the liquid crystal layer constituting the liquid crystal cell does not contain a chiral agent. As a result, in the liquid crystal display element having a d / p value of 0, the spiral twist included in the liquid crystal layer. It was also found that there was a concern about the occurrence of domain (non-uniform display) in which the palm of the structure was reversed, that is, there was a concern that right-handed and left-handed twisted structures would be mixed in the display surface of liquid crystal display elements . Therefore, from the viewpoint of ensuring display quality by preventing domain occurrence, it is preferable that d / p = 0 is not included in the range of the d / p value.

  In addition, a liquid crystal display device having a d / p value larger than 0.4 contains a relatively large amount of chiral agent, and there is a concern that the generation of domains due to an increase in the content of the chiral agent. I understood. Therefore, from the viewpoint of ensuring display quality by preventing domain occurrence, it is preferable that the range of d / p> 0.4 is not included in the range of d / p value.

Therefore, in consideration of realizing a display with a high contrast ratio and ensuring display quality by suppressing the generation of domains, the liquid crystal cell's natural twist pitch p and the pair of liquid crystal cells The distance d between the substrates is
0 <d / p ≦ 0.4
It is preferable to satisfy the relationship
0 <d / p ≦ 0.2
It is more preferable to satisfy this relationship.

  As described above, according to the liquid crystal display element of the present invention, there is almost no display unevenness due to rubbing scratches, excellent display quality and appearance, and display with a high contrast ratio is possible. Therefore, a liquid crystal display element having excellent display performance can be obtained.

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

2 is a schematic configuration diagram for explaining a structure and optical specifications of a liquid crystal display element in Embodiment 1. FIG. FIG. 6 is a schematic configuration diagram for explaining a structure and optical specifications of a liquid crystal display element that is a second comparative example of the first embodiment. In Embodiment 2, it is the figure which plotted CR value calculated | required with respect to the shift | offset | difference angle in a liquid crystal display element. In Embodiment 3, it is the figure which plotted the value of the largest CR calculated | required with respect to d / p value in a liquid crystal display element. It is a typical block diagram for demonstrating the structure and optical specification of the conventional VA mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20 Liquid crystal display element 2,21 Liquid crystal cell 3, 4, 22, 23 Polarizing plate 100 VA mode liquid crystal display element 101 Liquid crystal cell 102,103 Polarizing plate

Claims (6)

A liquid crystal cell sandwiching a liquid crystal layer made of liquid crystal having negative dielectric anisotropy between a pair of substrates that are aligned so that the liquid crystal has a pretilt angle of a predetermined angle and is vertically aligned substantially uniformly;
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 ° In
The liquid crystal is a chiral nematic liquid crystal containing a chiral agent and having a twist angle of 90 ° ± 5 ° between the substrates to constitute the liquid crystal layer,
The alignment treatment is a rubbing treatment for an alignment layer formed on the surface of the substrate,
The angle formed by one absorption axis of the polarizing plate and the rubbing direction in one of the substrates adjacent to the polarizing plate, and the other absorption axis of the polarizing plate and the substrate adjacent to the polarizing plate The liquid crystal display element is characterized in that the angle formed with the direction of the rubbing treatment on the other side is 0 ° or more and 7 ° or less.   The angle formed by one absorption axis of the polarizing plate and the rubbing direction in one of the substrates adjacent to the polarizing plate, and the other absorption axis of the polarizing plate and the substrate adjacent to the polarizing plate 2. The liquid crystal display element according to claim 1, wherein an angle formed with the direction of the rubbing treatment on the other side of the liquid crystal is 0 ° or more and 3 ° or less. Between the natural twist pitch p of the liquid crystal and the distance d between the substrates, 0 <d / p ≦ 0.4
The liquid crystal display element according to claim 1, wherein the relationship is established. 0 <d / p ≦ 0.2 between the natural twist pitch p of the liquid crystal and the distance d between the substrates.
The liquid crystal display element according to claim 1, wherein the relationship is established.   5. The liquid crystal cell according to claim 1, further comprising at least one retardation film having a negative retardation value in a thickness direction of the liquid crystal cell between at least one of the polarizing plates and the liquid crystal cell. A liquid crystal display element according to item.   The liquid crystal display element according to claim 1, wherein the liquid crystal display element is a passive matrix type liquid crystal display element.

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