JP2006106434A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a twisted nematic (TN) mode liquid crystal display element provided with characteristics such as an excellent black level, high contrast, a wide viewing angle, excellent steepness and the like. <P>SOLUTION: The liquid crystal display element has: a driving cell having upper side and lower side substrates equipped with electrodes, and a liquid crystal layer held in between and comprising liquid crystal molecules twist-aligned and having a helical structure in the state with no electric field; a compensating means disposed on a surface of one substrate of the driving cell and including upper side and lower side substrates, and a liquid crystal layer held in between and comprising liquid crystal molecules twist-aligned and having a helical structure, wherein, with respect to the liquid crystal layer, a twist direction of the helical structure is opposite to that of the helical structure in the driving cell, and the orientation direction of a liquid crystal molecule at the center of the liquid crystal layer and that in the driving cell vertically intersect with each other at right angles in surfaces of the upper side and lower side substrates; and two polarizing plates disposed on both sides of a structural body including the driving cell and the compensating means respectively in crossed Nicols, wherein both directions of transmission axes or absorption axes thereof are at 45° angle to the orientation direction of the liquid crystal molecule at the center of the liquid crystal layer of the driving cell in crossed Nicols disposition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display element, and more particularly to a twisted nematic (TN) mode liquid crystal display element.

  FIG. 10 is a schematic exploded perspective view showing a configuration of a main part of a conventional TN mode liquid crystal display element.

  The liquid crystal display element includes a liquid crystal cell 20 and polarizing plates 50 and 51.

  The liquid crystal cell 20 includes an upper substrate 11, a lower substrate 12 disposed to face the upper substrate 11 substantially in parallel, and a liquid crystal layer 15 held between the upper substrate 11 and the lower substrate 12. The liquid crystal layer 15 is filled with liquid crystal molecules 15a which are TN liquid crystals having a twist angle of 90 °.

  The upper substrate 11 includes, for example, a transparent substrate 11a which is a flat glass substrate, an electrode 11b formed of, for example, ITO (Indium Tin Oxide) on the transparent substrate 11a, and an alignment film 11c formed on the electrode 11b.

  The lower substrate 12 includes a transparent substrate 12a, an electrode 12b formed on the transparent substrate 12a, and an alignment film 12c formed on the electrode 12b. The material for forming the transparent substrate 12a, the electrode 12b, and the alignment film 12c is the same as the material for forming them on the upper substrate 11.

  The upper substrate 11 and the lower substrate 12 are arranged to face each other so that the alignment films 11c and 12c face each other.

  10 defines the angle coordinates representing the orientation direction (major axis direction) of the liquid crystal molecules at an azimuth angle θ rotated counterclockwise in a plane parallel to the lower substrate 12 with the right direction in FIG. 10 as a reference (0 °). To do.

  The alignment films 11c and 12c of the upper substrate 11 and the lower substrate 12 are rubbed. The rubbing direction D1 applied to the alignment film 11c of the upper substrate 11 is an azimuth angle of 45 °, and the rubbing direction D2 applied to the alignment film 12c of the lower substrate 12 is an azimuth angle of 315 ° (−45 °). ) Direction. The liquid crystal molecules 15a in contact with the alignment films 11c and 12c are aligned parallel to the rubbing direction and tilted so that the end portion on the tip side of the arrow indicating the rubbing direction is lifted from the substrate. Since the alignment films are arranged to face each other, the end of the liquid crystal molecules 15a on the lower substrate 12 side that is lifted from the substrate corresponds to the end of the liquid crystal molecules 15a on the upper substrate 11 side that contacts the substrate. Tilt so that.

  The liquid crystal molecules 15a in the liquid crystal layer 15 are twisted in the azimuth direction to form a helical structure. This helical structure turns counterclockwise, the twist angle (twist angle, turn angle) is 90 °, and the azimuth angle θ in the alignment direction of the liquid crystal molecules located at the center in the thickness direction is 270 °.

  The polarizing plate 50 is in close contact with the outer surface of the upper substrate 11 of the liquid crystal cell 20, and the polarizing plate 51 is in close contact with the outer surface of the lower substrate 12. The azimuth angle θ in the transmission axis direction D3 of the polarizing plate 50 is 45 °, and the azimuth angle θ in the transmission axis direction D4 of the polarizing plate 51 is also 45 °. The polarizing plates 50 and 51 are arranged in parallel Nicols.

  In a state where no voltage is applied, the liquid crystal molecules 15a are TN aligned. The light that has passed through the polarizing plate 51 and entered the lower substrate 12 travels in the liquid crystal layer 15 while rotating the polarization direction along the director of the liquid crystal molecules 15a, and is emitted from the upper substrate 11 when rotated 90 °. It is blocked by the polarizing plate 50 on the upper substrate 11 side. For this reason, black display is realized.

  When a voltage is applied, the liquid crystal molecules 15a stand perpendicular to the substrates (the upper substrate 11 and the lower substrate 12). Therefore, the light transmitted through the polarizing plate 51 and incident on the lower substrate 12 passes through the liquid crystal layer 15 as it is. Then, the light is emitted from the upper substrate 11 and the polarizing plate 50. In this case, white display is realized.

  In such a normally black 90 ° twisted TN mode liquid crystal display element, a thickness d (μm) of the liquid crystal layer 15 is used to obtain a good black level (good off display with low light transmittance) when no voltage is applied. ) And the product Δnd (retardation, unit μm) of the birefringence Δn of the liquid crystal material forming the liquid crystal layer 15 must be adjusted appropriately.

  FIG. 11 is a graph showing the relationship between retardation Δnd and light transmittance when no voltage is applied. The horizontal axis represents retardation Δnd in the unit “μm”. The vertical axis indicates the light transmittance in the unit “%”.

  When the retardation Δnd is about 0.49 μm and about 1 μm, the light transmittance takes a minimum value. This shows a change in light transmittance according to the so-called Gooch & Tarry equation. When the retardation Δnd exceeds about 1 μm, there is no noticeable increase or decrease in the light transmittance, and the light transmittance decreases monotonously in the range where the retardation Δnd is about 1.9 μm or more. Therefore, at least at a retardation Δnd of a certain value or more, the retardation Δnd gives a light transmittance lower than the light transmittance when the retardation Δnd is about 0.49 μm (first minimum condition) and about 1 μm (second minimum condition), It can be seen that a good black display can be realized.

  However, when the value of retardation Δnd is increased (for example, retardation Δnd equal to or higher than the second minimum condition), the thickness of the liquid crystal layer 15 increases, and the response speed of the liquid crystal molecules 15a becomes low. Moreover, the problem that a drive voltage rises arises. Further, the method of obtaining a good black display by increasing the retardation Δnd is an effective method only when the twist angle of the liquid crystal molecules is 90 °.

  As can be seen from the graph shown in FIG. 11, it is difficult to obtain a good black level in the normally black TN liquid crystal display element shown in FIG. It is. Since a good black level can be obtained only by the minimum condition of Gooch & Tarry, there is a great restriction on design. Moreover, it is usually difficult to obtain a good black level even when the retardation Δnd is about 0.49 μm in order to produce a high-speed response liquid crystal display element in which the twist angle is set to 90 °. In addition, since the influence of gap fluctuation is large, the viewing angle becomes narrow, and further, it is difficult to manufacture a cell having a uniform thickness. Therefore, in reality, the retardation of 0.49 μm is hardly used in practice.

  In the normally white type liquid crystal display element that is currently used, since a black display is realized when a voltage is applied, a relatively high applied voltage (drive voltage) must be set to obtain a good black display. . Further, in the case of a liquid crystal display element driven by a simple matrix, if the number of scans is increased with an emphasis on the transmittance of bright display, the black level increases accordingly, and a clear display contrast may not be obtained.

A liquid crystal display device having a “two-layer structure in which a conventional single-layer twisted nematic field effect type liquid crystal display cell is superposed with a twisted nematic liquid crystal layer that does not have a power supply means” has been invented. (For example, see Patent Document 1.)
The two-layer type liquid crystal display device disclosed in Patent Document 1 is a so-called twisted type in which the major axis of the liquid crystal molecule is twisted by 90 ° between the substrates with the spiral axis in the direction perpendicular to the substrate surface. The present invention relates to a nematic field effect type liquid crystal display device, and particularly relates to a technique for reducing the coloring phenomenon of the display when it is inactive.

JP-A-57-96315

  An object of the present invention is to provide a high-quality liquid crystal display element.

  According to one aspect of the present invention, there are provided an upper substrate and a lower substrate each having an electrode, and a liquid crystal layer that is held between the two substrates and has a helical structure in which liquid crystal molecules are twisted in a state where no electric field is generated. A driving cell having a liquid crystal layer disposed on one of the substrate surfaces of the driving cell, held between the upper substrate and the lower substrate, and having a helical structure in which liquid crystal molecules are twisted and arranged, The liquid crystal layer has a helical structure swirling direction opposite to the driving cell helical structure swiveling direction, and the liquid crystal molecule alignment direction positioned in the center with respect to the thickness direction of the liquid crystal layer; Compensation means in which the alignment direction of the liquid crystal molecules located in the center with respect to the thickness direction of the liquid crystal layer is orthogonal in the planes of the upper and lower substrates, respectively, on both sides of the structure including the drive cell and the compensation means Black Two polarizing plates arranged in Nicol, the direction of the transmission axis or the absorption axis are both 45 ° angle with the alignment direction of the liquid crystal molecules located in the center with respect to the thickness direction of the liquid crystal layer of the drive cell There is provided a liquid crystal display element having two polarizing plates arranged in crossed Nicols so as to form the following.

  This liquid crystal display element is a liquid crystal display element that can have characteristics such as a good black level, high contrast, a wide viewing angle, and good steepness.

  According to the present invention, a high-quality liquid crystal display element can be provided.

  In the above proposal (Japanese Patent Application No. 2003-287054, [Best Mode for Carrying Out the Invention] [0012] to [0054] and FIGS. 1 to 11), the inventors of the present application describe that an electric field is generated. A driving cell in which an electrode for generating an electric field in the in-plane direction of the substrate is formed on the liquid crystal layer, the liquid crystal layer holding a liquid crystal layer having a helical structure with twisted alignment of liquid crystal molecules, and one surface of the driving cell A liquid crystal layer having a helical structure in which the liquid crystal molecules are twisted and arranged in a twisted direction, and the rotational direction of the helical structure is opposite to the rotational direction of the helical structure of the drive cell, and the thickness of the liquid crystal layer Compensation means in which the alignment direction of the liquid crystal molecules located in the center with respect to the direction is orthogonal to the alignment direction of the liquid crystal molecules located in the center with respect to the thickness direction of the liquid crystal layer of the drive cell, and the drive cell and the compensation means On both sides of the body The liquid crystal display device "(Japanese Patent Application No. 2003-287054, [Claim 1]) and a polarizing plate disposed Re respectively disclosed in detail invention such.

  In the present application, a liquid crystal display element related to this is proposed.

  FIG. 1 is a schematic exploded perspective view showing a configuration of a main part of a liquid crystal display element according to an embodiment. FIG. 1 shows an example of a liquid crystal display element having a twist angle of 90 °. The liquid crystal display element according to the embodiment includes a driving cell 30, a compensation cell 40, a polarizing plate 53 on the driving cell 30 side, and a polarizing plate 52 on the compensation cell 40 side.

  The configuration of the drive cell 30 is the same as that of the liquid crystal cell 20 shown in FIG.

  The compensation cell 40 includes an upper substrate 31, a lower substrate 32, and a liquid crystal layer 35 sandwiched between them. The lower substrate 32 is in contact with the upper substrate 21 of the drive cell 30. Alignment films 31c and 32c are formed on the opposing surfaces of the upper substrate 31 and the lower substrate 32, respectively, and subjected to a rubbing process. The rubbing direction D7 applied to the alignment film 31c of the upper substrate 31 is an azimuth angle of 225 °, and the rubbing direction D8 applied to the alignment film 32c of the lower substrate 32 is an azimuth angle of 315 ° (−45 °). ) Direction.

  The liquid crystal layer 35 is filled with, for example, a liquid crystal material having positive uniaxial optical anisotropy. The liquid crystal molecules 35a in the liquid crystal layer 35 are twisted to form a helical structure. This helical structure turns right, the twist angle is 90 °, and the azimuth angle θ in the alignment direction of the liquid crystal molecules located at the center in the thickness direction is 0 °. The alignment direction (270 °) of the liquid crystal molecules 25a positioned in the center with respect to the thickness direction of the liquid crystal layer 25 of the driving cell 30 and the alignment direction of the liquid crystal molecules 35a positioned in the center with respect to the thickness direction of the liquid crystal layer 35 of the compensation cell 40. (0 °) are orthogonal to each other in the in-plane direction of the substrate.

  In both the drive cell 30 and the compensation cell 40, the alignment direction of the liquid crystal molecules located in the center with respect to the thickness direction of the liquid crystal layer is determined by the unit vector in the in-plane direction of the rubbing treatment applied to the upper substrate, This is a direction orthogonal to the direction of the combined vector of the unit vectors in the in-plane direction of the rubbing process applied to the side substrate. Therefore, the orientation directions of the liquid crystal molecules at the central position with respect to the thickness direction of the liquid crystal layer of the driving cell and the compensation cell are orthogonal to each other when the direction of the synthetic vector in the driving cell 30 and the direction of the synthetic vector in the compensation cell 40 are. And are orthogonal to each other.

  The polarizing plate 52 is in close contact with the outer surface of the upper substrate 31 of the compensation cell 40, and the polarizing plate 53 is in close contact with the outer surface of the lower substrate 22 of the driving cell 30. The azimuth angle θ in the transmission axis direction D9 of the polarizing plate 52 is 135 °, and the azimuth angle θ in the transmission axis direction D10 of the polarizing plate 53 is 45 °. The polarizing plates 52 and 53 are arranged in crossed Nicols.

  Both the directions of the transmission axes of the upper and lower polarizing plates 52 and 53 form an angle of 45 ° with the alignment direction of the liquid crystal molecules 25 a located in the center with respect to the thickness direction of the liquid crystal layer 25 of the drive cell 30.

  The liquid crystal display element according to the embodiment is a liquid crystal display element that performs black display when no voltage is applied and white display when a voltage is applied.

  Hereinafter, the simulation result which examined the conditions from which the favorable display state is obtained about the liquid crystal display element by an Example is shown. All simulations were performed using an LCD MASTER 6.02 one-dimensional simulator manufactured by Shintech. The liquid crystal material assumed was ZLI-4792 manufactured by Merck, and the polarizing plate assumed was G1220U manufactured by Nitto Denko, or KN-18242T manufactured by Polatechno. In addition, a chiral agent is added to the liquid crystal material, and the liquid crystal molecules are twisted in the same direction as the twist direction set by the alignment film.

  When the twist angle was 120 ° or less, the ratio d / p between the cell thickness d and the chiral pitch p was adjusted to 0.1. When the twist angle was larger than that, the d / p was adjusted to be 0.2. The alignment film was set to give a pretilt angle of 0.5 °.

  FIG. 2 is a graph showing the results of calculating the spectrum of the liquid crystal display element in front of the visible light region when no twist is applied, with the twist angle fixed at 90 ° and the retardation Δnd fixed at 0.5 μm (cell thickness 5 μm). It is.

  The horizontal axis of the graph indicates the wavelength in the unit “nm”. The vertical axis indicates the light transmittance in “arbitrary units”. The curve a is the simulation result for the liquid crystal display element according to the conventional example shown in FIG. 10, and the curve b is the simulation result for the liquid crystal display element according to the embodiment shown in FIG.

  Refer to curve a. It can be seen that in the liquid crystal display element according to the conventional example, light leakage occurs on the short wavelength side having a peak of about 440 nm and on the long wavelength side of about 570 nm or more. Actually, a sample of a liquid crystal display element according to the conventional example was manufactured and observed using the same materials and conditions as in the simulation, and when the voltage was not applied in the sample, the display state was purple, and light leakage occurred. It was confirmed that

  Refer to curve b. It can be seen that in the liquid crystal display elements according to the examples, almost no light leakage occurs in all wavelength regions. Actually, a sample of the liquid crystal display element according to the example was manufactured and observed under the same materials and conditions as in the simulation, and it was confirmed that a good black level was obtained when no voltage was applied in the sample. .

  In addition, in the liquid crystal display element by an Example, if the difference of retardation (DELTA) nd between a drive cell and a compensation cell was less than 0.3 micrometer, it confirmed that a favorable black level was obtained.

  Next, for the liquid crystal display element according to the example, simulation was performed on the cell thickness dependence of the viewing angle characteristics in the black level state when no voltage was applied.

  3A to 3E show isoluminous curves when no voltage is applied to five retardation values of 0.44 μm or more and 0.8 μm or less at a twist angle of 90 °. (A) is when retardation is 0.44 μm (cell thickness is 4.4 μm), (B) is when 0.55 μm (cell thickness is 5.5 μm), and (C) is 0.65 μm (cell) When (thickness is 6.5 μm), (D) is an isoluminance curve when 0.75 μm (cell thickness is 7.5 μm) and (E) is 0.8 μm (cell thickness is 8 μm). . The simulation was performed assuming that the cell thickness of the driving cell and the compensation cell were equal. In the simulation described below, KN-18242T was assumed as the polarizing plate.

  From the isoluminance curves of FIGS. 3 (A) to (E), as the cell thickness (retardation) increases, the loss of light when the viewing angle is greatly shaken is reduced, and the cell thickness is about 7.5 to 8 μm (retardation is reduced). It can be seen that a state with the least light leakage is obtained at about 0.75 to 0.8 μm.

  Note that the black level when observed from the front of the element was the same for all cell thickness settings, and was equivalent to a crossed Nicol arrangement of a pair of polarizing plates. Furthermore, as a result of repeating the simulation, when observed from an azimuth of 0 ° or 180 ° and a polar angle of 60 ° (when the cell normal is 0 °), the transmittance when no voltage is applied (black level transmittance) is approximately It was also found that the cell thickness was 6.3 μm or more and 10 μm or less under the conditions that can be suppressed to 4% or less.

  The liquid crystal display element according to the embodiment is a normally black TN liquid crystal display element capable of realizing a good off display without restriction of retardation Δnd due to the Gooch & Tarry minimum condition. Compared with the conventional TN mode liquid crystal display element according to the Gooch & Tarry equation, the cell thickness setting is arbitrary, and the degree of freedom in cell design is large. A good black level can be obtained by frontal observation when no voltage is applied over a wide range of cell thicknesses.

  Subsequently, for the liquid crystal display element according to the example, the electro-optical characteristic when observed from the front of the element is calculated, the light transmittance when the applied voltage is 5 V, and the cell thickness of the sharpness of the curve in the electro-optical characteristic. The dependence was examined. In the evaluation of the steepness, when the light transmittance at an applied voltage of 5 V is 100%, a voltage at which 90% transmittance is obtained is defined as “V90”, and a voltage at which 5% transmittance is obtained is defined as “V90”. V5 "and their ratio" V90 / V5 "was used.

  FIG. 4 is a graph showing changes in light transmittance at an applied voltage of 5 V and cell thickness of “V90 / V5”. The horizontal axis indicates the cell thickness in the unit “μm”, and the vertical axis indicates the transmittance and “V90 / V5” in the units “%” and “arbitrary unit”, respectively.

  The curve a is a curve showing the light transmittance when 5 V is applied. The curve of b shows “V90 / V5”.

  Refer to curve a. When the cell thickness is about 8 μm, the transmittance is the lowest. The cell thickness of 8 μm is a value described with reference to FIGS. 3A to 3E to belong to the range where the viewing angle characteristic of the black level is the best.

  Refer to curve b. As the cell thickness increases, the value of “V90 / V5” also increases. This indicates that the steepness deteriorates as the cell thickness increases.

  From the two curves, it is understood that it is not preferable to set a large cell thickness when importance is attached to the transmittance at the time of voltage application.

  It is considered effective to change the setting of the torsion angle in order to increase the light transmittance during voltage application and improve the steepness. The inventors first set several twist angles (90 °, 100 °, 110 °, 120 °, 130 °, 140 °, 150 °, and 160 °), and at each twist angle, a good voltage was set. The cell thickness conditions under which viewing angle characteristics were obtained when no voltage was applied were investigated. The viewing angle characteristics were evaluated by examining the cell thickness dependence of the light transmittance at an azimuth of 180 ° and a polar angle of 60 ° for each twist angle.

  FIG. 5 is a graph showing light transmittance when no voltage is applied, when the liquid crystal display element according to the example and the liquid crystal display element that is different only in the twist angle are observed from an azimuth of 180 ° and a polar angle of 60 °. is there.

  The horizontal axis indicates the thickness of the cell (driving cell and compensation cell) in the unit “μm”. The vertical axis indicates the transmittance in the unit “%”. Curves were created for each twist angle of liquid crystal molecules in the driving cell.

  A curve with white circles connected by a solid line has a twist angle of 90 °, a curve with white circles connected by a dotted line has a twist angle of 110 °, and a curve with white circles connected by a solid line has a twist angle of 110 °. If the twist angle is 120 °, the curve connecting the white triangles with the solid line is the curve connecting the white triangles with the dotted line when the twist angle is 130 °. When the angle is 140 °, a curve in which the cross mark is connected by a solid line indicates a simulation result in the case where the twist angle is 150 °, and a curve in which the cross mark is connected by a dotted line shows a simulation result when the twist angle is 160 °.

  It can be seen that the cell thickness condition for obtaining a transmittance of about 4% or less in the range of the twist angle of 90 ° or more and 150 ° or less is 6.5 μm or more and 9.5 μm or less.

  For example, when the twist angle is 90 °, the cell thickness is about 8 μm and the transmittance is minimum, and the value (minimum transmittance) is about 1%. With respect to this point, the inventors of the present invention further obtained and graphed the minimum value (minimum transmittance) of the transmittance at each twist angle and the cell thickness that gives the minimum value from FIG.

  FIG. 6 is a graph showing the twist angle dependency of the minimum transmittance and the twist angle dependency of the cell thickness giving the minimum transmittance. The curve a represents the former relationship, and the curve b represents the latter relationship.

  The horizontal axis indicates the twist angle in the unit “°”. The vertical axis indicates the minimum transmittance and the cell (driving cell and compensation cell) thickness giving the minimum transmittance in units of “%” and “μm”, respectively.

  Refer to curve a. It can be seen that the minimum transmittance is maximized when the twist angle is 130 °.

  Refer to curve b. It can be seen that the cell thickness at which the minimum transmittance is obtained increases almost linearly as the twist angle increases.

  Based on the above results, the inventors of the present application applied the voltage of 5 V to the liquid crystal display element according to the embodiment and the drive cell (between the electrodes of the upper and lower substrates) of the liquid crystal display element that differs only in the twist angle. The cell thickness dependence of the transmittance during frontal observation under each twist angle condition was calculated.

  FIG. 7 is a graph showing light transmittance when a voltage of 5 V is applied to the liquid crystal display element according to the example and the driving cell of the liquid crystal display element that is different only in the twist angle and the liquid crystal display element is observed from the front. is there.

  The horizontal axis indicates the cell (driving cell and compensation cell) thickness in the unit of “μm”. The vertical axis indicates the transmittance in the unit “%”. Curves were created for each twist angle (90 °, 100 °, 110 °, 120 °, 130 °, 140 °, 150 °) of liquid crystal molecules in the driving cell. The display method of the curve is the same as in the case of FIG. 5. For example, a curve in which white circles are connected by a solid line indicates a simulation result when the twist angle is 90 °.

  It can be seen that at a helix angle of 100 ° to 130 ° (100 °, 110 °, 120 °, 130 °), the change in transmittance with respect to the change in cell thickness is smaller than that at a helix angle of 90 °.

  Based on the above considerations, conditions for the cell thickness and twist angle of a liquid crystal display device that has good transmittance when a voltage is applied and has excellent viewing angle characteristics (black level viewing angle characteristics) when no voltage is applied. To decide.

  FIG. 8 is a chart showing the transmittance at the time of applying 5 V, the transmittance at an azimuth of 180 °, and a polar angle of 60 ° when no voltage is applied under the conditions determined by the cell thickness and the twist angle.

  The horizontal axis indicates the cell thickness in the unit “μm”, and the vertical axis indicates the twist angle in the unit “°”. In each condition in the figure, the upper numerical value indicates the transmittance when 5 V is applied, and the lower numerical value indicates the transmittance when no voltage is applied. For example, under the conditions of a cell thickness of 6.5 μm and a twist angle of 90 °, the transmittance when 5 V is applied is 27.1%, and the transmittance when no voltage is applied is 3.86%. FIG. 8 shows only the conditions under which the transmittance when applying 5 V is 27% or more and the transmittance when no voltage is applied is 4% or less.

  From FIG. 8, when the cell thickness is 6.5 μm or more and 9.5 μm or less and the twist angle is 90 ° or more and 150 ° or less, the cell thickness is preferably 7.5 μm or more and 9.5 μm or less and the twist angle is 110 ° or more. When the angle is 130 ° or less, it is considered that good display performance can be realized. When the preferable cell thickness range is expressed by retardation Δnd, it is 0.65 μm or more and 0.95 μm or less, and more preferably 0.75 μm or more and 0.95 μm or less.

  By setting the cell thickness (or retardation) or torsion angle within the above range, the transmittance when applying voltage is not significantly reduced (while maintaining a relatively high ON transmittance), and black when no voltage is applied. A liquid crystal display element having a good level and excellent display performance can be obtained.

  The preferred retardation Δnd is much smaller than that of a normally black TN liquid crystal display element that can obtain a good black level. For this reason, the cell thickness of a liquid crystal display element can be made thin and the fall of a response speed can be prevented.

  Next, the inventors of the present application examined the cell thickness dependence of each twist angle condition of “V90 / V5” (a measure representing steepness in electro-optical characteristics during frontal observation). When “V90 / V5” is large, the applied voltage (drive voltage) is reduced.

  FIG. 9 is a graph showing the cell thickness dependence of “V90 / V5”.

  The horizontal axis indicates the cell (driving cell and compensation cell) thickness in the unit of “μm”. The vertical axis indicates “V90 / V5” in “arbitrary units”. Curves were created for each twist angle (90 °, 100 °, 110 °, 120 °, 130 °, 140 °, 150 °, 160 °) of liquid crystal molecules in the driving cell. The display method of the curve is the same as in the case of FIG. 5. For example, a curve in which white circles are connected by a solid line indicates a simulation result when the twist angle is 90 °.

  It can be seen that as the twist angle increases, the value of “V90 / V5” decreases and the steepness is improved. Also, when the twist angle is up to 140 °, the steepness tends to deteriorate as the cell thickness increases, but when the twist angle is 150 ° or more, the opposite tendency is observed. From this, the optical operation principle of the liquid crystal display element tends to be different between the case where the twist angle is less than 150 ° and the case where the twist angle is 150 ° or more. In the range of 150 ° or more, the so-called twist angle is 180 ° or more. It is considered that the operation is equivalent to that in the super twist nematic (STN) mode. The STN mode generally tends to be difficult to handle due to a large change in display characteristics with respect to a change in cell thickness. Therefore, it may be preferable to set the twist angle to less than 150 °.

  The liquid crystal display element according to the embodiment is a normally black TN liquid crystal display element with a wide viewing angle, high contrast, and good steepness.

  In the embodiment, the liquid crystal director has a twist direction opposite to the twist direction of the drive cell 50 between the upper substrate 41 of the drive cell 50 and the polarizing plate 64 and in the center of the thickness direction in the liquid crystal layer. Compensation cells 60 whose orientations are orthogonal to each other in the in-plane direction of the substrate are arranged. Since the alignment state of the liquid crystal molecules 55a in the liquid crystal layer 55 of the compensation cell 60 does not change during operation, an optical film or a plastic film made of a liquid crystal polymer or the like having equivalent optical characteristics is used instead of the compensation cell 60. May be. For example, an optical film having liquid crystallinity, such as Polatechno (manufactured by Deima) Twistar film, can be preferably used. A simulation was also performed on a liquid crystal display element using a Twistar film instead of the compensation cell 60, and the same result as the above-mentioned result was obtained.

  Further, the arrangement of the drive cell 50 and the compensation cell 60 may be exchanged.

  In the liquid crystal display device according to the example, the alignment of the liquid crystal molecules in the driving cell was made uniform (monodomain alignment). It is also possible to adopt a multi-domain structure in which the liquid crystal molecules of the driving cell have different orientation directions depending on the location (the liquid crystal display element includes a liquid crystal layer having a plurality of orientation directions depending on the location). The multi-domain structure can be realized by a method of performing alignment processing by photo-alignment on the alignment film of the driving cell, a method of generating an oblique electric field in the liquid crystal layer using an electrode having a slit in the driving cell, and the like.

  By adopting the multi-domain structure, the viewing angle characteristics can be further improved as compared with the case of adopting the mono-domain structure. In particular, the viewing angle symmetry at the time of bright display can be improved.

  Further, among the liquid crystal display elements according to the present application, particularly for a liquid crystal display element driven by simple matrix, it is possible to obtain a good display quality under a low duty (1/4 to 1/16 duty) condition, which has been difficult in the past. Is possible. In conventional twisted nematic liquid crystal display elements, there are few conditions for obtaining a good black level, and the steepness in electro-optical characteristics is poor, so that only about less than 1/4 duty has been put to practical use. Moreover, the twist angle could not be set to other than 90 °. However, as shown in FIG. 9, the liquid crystal display element according to the present application can control the steepness by changing the twist angle, and can also improve the black level and the viewing angle characteristics. .

  As mentioned above, although this invention was demonstrated along the Example, this invention is not restrict | limited to these. For example, in the examples, the transmission axis directions of the upper and lower polarizing plates are both at an angle of 45 ° with the alignment direction of the liquid crystal molecules located in the center with respect to the thickness direction of the liquid crystal layer of the driving cell. However, the two polarizing plates may be arranged in a crossed Nicol manner so that the direction of the absorption axis of the polarizing plate is as described above. It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.

  (I). A statically driven liquid crystal display element, (ii). Segment display simple matrix drive liquid crystal display element, (iii). Dot matrix display simple matrix drive liquid crystal display element, (iv). A liquid crystal display element incorporating (ii) and (iii) in one element, (v). The present invention can be applied to an active matrix drive liquid crystal display element including a thin film transistor (TFT) drive.

It is a schematic exploded perspective view which shows the structure of the principal part of the liquid crystal display element by an Example. It is a graph which shows the result of having calculated the spectrum at the time of liquid crystal display element front observation of the visible light area | region at the time of fixing a twist angle to 90 degrees and retardation (DELTA) nd to 0.5 micrometer (cell thickness 5 micrometers), and no voltage application. (A) to (E) show isoluminance curves when no voltage is applied to five retardation values of 0.44 μm to 0.8 μm at a twist angle of 90 °. It is a graph which shows the change with respect to the light transmittance at the time of applied voltage 5V, and the cell thickness of V90 / V5. It is a graph showing the light transmittance at the time of no voltage application at the time of observing the liquid crystal display element by an Example, and the liquid crystal display element from which only a twist angle differs from azimuth | direction 180 degrees and polar angles 60 degrees. It is a graph showing the twist angle dependency of the minimum transmittance, and the twist angle dependency of the cell thickness giving the minimum transmittance. It is a graph showing the light transmittance at the time of applying the voltage of 5V to the liquid crystal display element by an Example, and the drive cell of the liquid crystal display element from which only a twist angle differs, and observing a liquid crystal display element from the front. It is a graph which shows the transmittance | permeability at the time of 180 degrees of azimuth | direction at the time of no application of a voltage, and a polar angle of 60 degrees at the time of 5 V application in the conditions defined by cell thickness and a twist angle. It is a graph which shows the cell thickness dependence of "V90 / V5". It is a schematic exploded perspective view which shows the structure of the principal part of the conventional TN mode liquid crystal display element. It is a graph showing the relationship between retardation Δnd and light transmittance when no voltage is applied.

Explanation of symbols

11, 21, 31 Upper substrate 12, 22, 32 Lower substrate 11a, 12a, 21a, 22a, 31a, 32a Transparent substrate 11b, 12b, 21b, 22b Electrode 11c, 12c, 21c, 22c, 31c, 32c Alignment film 15 , 25, 35 Liquid crystal layer 15a, 25a, 35a Liquid crystal molecule 20 Liquid crystal cell 30 Drive cell 40 Compensation cell 50, 51, 52, 53 Polarizing plate D1-D10 direction

Claims (9)

A driving cell having an upper substrate and a lower substrate each provided with an electrode, and a liquid crystal layer that is held between the liquid crystal layers and has a helical structure in which liquid crystal molecules are twisted in a state where no electric field is generated;
A liquid crystal layer disposed on one of the substrate surfaces of the driving cell, held between the upper substrate and the lower substrate, and having a helical structure in which liquid crystal molecules are twisted, and the liquid crystal layer has a helical structure; The turning direction of the structure is opposite to the turning direction of the helical structure of the drive cell, and the orientation direction of the liquid crystal molecules located in the center with respect to the thickness direction of the liquid crystal layer and the thickness of the liquid crystal layer of the drive cell Compensation means in which the alignment direction of the liquid crystal molecules located in the center with respect to the direction is orthogonal in the plane of the upper and lower substrates,
Two polarizing plates disposed in crossed Nicols on both sides of the structure including the driving cell and the compensation means, both of which have a transmission axis or an absorption axis in the thickness of the liquid crystal layer of the driving cell A liquid crystal display element having two polarizing plates arranged in a crossed Nicol so as to form an angle of 45 ° with an alignment direction of liquid crystal molecules located in the center with respect to the direction. The liquid crystal display element according to claim 1, wherein the magnitude of the turning angle of the helical structure of the drive cell is equal to the magnitude of the turning angle of the helical structure of the compensation means. 3. The liquid crystal display element according to claim 1, wherein a magnitude of a turning angle of the helical structure of the driving cell and the compensation means is 90 ° or more and 150 ° or less. 3. The liquid crystal display element according to claim 1, wherein the rotational angle of the helical structure of the driving cell and the compensating means is 110 ° or more and 130 ° or less. The liquid crystal display element according to claim 1, wherein the retardation of the liquid crystal layer of the driving cell is 0.65 μm or more and 0.95 μm or less. The liquid crystal display element according to claim 1, wherein the retardation of the liquid crystal layer of the driving cell is 0.75 μm or more and 0.95 μm or less. The liquid crystal display element according to claim 1, wherein a difference between the retardation of the liquid crystal layer of the driving cell and the retardation of the liquid crystal layer of the compensation means is 0.3 μm or less. The liquid crystal display element according to claim 1, wherein the driving cell has a multi-domain structure. The liquid crystal display element according to claim 1, wherein the liquid crystal layer of the compensation means is formed of a liquid crystal material having positive uniaxial optical anisotropy.