JP2011164274A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element which is capable of achieving satisfactory display. <P>SOLUTION: The liquid crystal display element includes: first and second transparent substrates; an approximately vertically aligned liquid crystal layer which is held between the first and second transparent substrates and has retardation of 300 to 1,200 nm; first and second optical films disposed on the side opposite to the liquid crystal layer side, of the first transparent substrate; a first polarizing plate disposed on the side opposite to the first transparent substrate side, of the first and second optical films; and a second polarizing plate disposed on the side opposite to the liquid crystal layer side, of the second transparent substrate. In this configuration, an in-plane slow axis of the first optical film and an absorption axis of the first polarizing plate are orthogonal, and the in-plane slow axis of the first optical film and an in-plane slow axis of the second optical film are orthogonal, and a phase difference in the in-plane direction of the first optical film is larger than that of the second optical film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid crystal display (LCD).

  A normally black liquid crystal display element with very low display brightness in the background display section and dark display section is mounted on a liquid crystal display device capable of segment display or segment display and dot matrix display that operate by multiplex drive. A lot is happening. Most of them are monochrome displays using a single color LED as a backlight, and a twisted nematic (TN) type is adopted as a liquid crystal display element structure.

  Vertical alignment in which a liquid crystal cell in a vertical alignment mode in which the liquid crystal molecular alignment in the liquid crystal layer is aligned perpendicularly or substantially perpendicular to the upper and lower glass substrates sandwiching the liquid crystal layer is disposed between polarizing plates arranged substantially in crossed Nicols. Type liquid crystal display elements are known. When viewed from the normal direction of the glass substrate, the vertical alignment type liquid crystal display element has almost the same optical characteristics as a polarizing plate with a crossed Nicol arrangement, so the light transmittance is very low and the high contrast ratio is relatively low. It can be easily realized. The vertically aligned liquid crystal display element enables good normally black display independent of the emission wavelength of the backlight.

  Optical film having negative uniaxial optical anisotropy or optical having negative biaxial optical anisotropy between one or both of the upper polarizing plate and the upper glass substrate and between the lower polarizing plate and the lower glass substrate An invention of a liquid crystal display element in which a film (a negative biaxial film) is disposed is disclosed (for example, see Patent Document 1). According to this liquid crystal display element, even when observed from an oblique direction, an increase in light transmittance and a decrease in contrast ratio are suppressed, and a good display can be realized.

  Regarding the viewing angle compensation method described in Patent Document 1, effective conditions relating to the in-plane retardation and in-plane slow axis arrangement of a negative biaxial film have been proposed (for example, see Patent Document 2).

  As an optical film having negative uniaxial optical anisotropy (negative C plate), it is used as a protective film for polarizing plates, a resin formed into a film by a melt casting method, such as triacetyl cellulose (TAC), or melted A biaxially stretched film obtained by stretching a norbornene-based cyclic olefin polymer (norbornene COP) resin formed into a film by an extrusion method in the film extrusion direction and its orthogonal direction is commercially available.

  Examples of the negative biaxial film include a film obtained by uniaxially stretching a special TAC resin in a direction orthogonal to the film longitudinal direction, and a film obtained by biaxially stretching norbornene COP. These are used, for example, in liquid crystal televisions, and are distributed in larger quantities than negative C plates.

  When the negative C plate is a TAC film, the retardation Rth in the thickness direction of the available film is almost 50 nm or less. Further, even in the case of norbornene COP, the retardation Rth in the thickness direction of an available film is 300 nm or less. An optical film having an Rth greater than 300 nm is known to be produced using, for example, a cholesteric liquid crystal polymer, but is not commercially available at present.

  For negative biaxial films, the in-plane retardation Re of the available stretched TAC is 0 nm <Re ≦ 60 nm, that of norbornene COP is 0 nm <Re ≦ 700 nm, and the retardation Rth in the thickness direction is the stretched TAC 50 ≦ Rth ≦ 220 nm, and norbornene COP is about 90 ≦ Rth ≦ 500 nm.

  Hereinafter, before explaining in detail the liquid crystal display elements according to the conventional examples and the examples, the optical film will be supplementarily described.

  In the case of an optical film having negative uniaxial optical anisotropy (negative C plate) where nx and ny are the in-plane refractive indexes of the flat optical film and nz is the refractive index in the thickness direction, nx≈ny> In an optical film having negative biaxial optical anisotropy (negative biaxial film), there is a relationship of nx> ny> nz.

  When the Nz factor is defined as Nz = (nx−nz) / (nx−ny), the negative uniaxial optical anisotropy is Nz≈∞, and the negative biaxial optical anisotropy is 1 <Nz <. ∞.

  In the case of Nz = 1, positive uniaxial optical anisotropy is shown, and an optical film having positive uniaxial optical anisotropy is called an A plate. In the A plate, nx> ny = nz. In addition, Nz <1 mainly shows positive biaxial optical anisotropy, but Nz = 0 and Nz = −∞ are excluded because there is only one optical axis. An optical film with Nz = 0 is called a negative A plate, and an optical film with Nz = −∞ is called a positive C plate.

  The in-plane retardation Re of the optical film is Re = (nx−ny) * d when the film thickness is d, and the retardation Rth in the thickness direction is Rth = [{(nx−ny) / 2}. -Nz] * d.

  9A and 9B are schematic views showing a liquid crystal display element according to a conventional example. Patent Document 2 discloses a technique that assumes the structure of these liquid crystal display elements.

  FIG. 9A shows an outline of the liquid crystal display element according to the first conventional example.

  A monodomain vertical alignment liquid crystal cell 30 is disposed between the upper polarizing plate 10 and the lower polarizing plate 20 that are arranged in crossed Nicols. The monodomain vertical alignment liquid crystal cell 30 includes an upper glass substrate (transparent substrate) 4, a lower glass substrate (transparent substrate) 6, and a monodomain vertical alignment liquid crystal layer 5 sandwiched between the substrates 4 and 6. Is done. Between the upper glass substrate 4 and the upper polarizing plate 10 of the vertical alignment liquid crystal cell 30, for example, one first optical film 3 that is a norbornene COP biaxially stretched film is disposed.

  Each of the upper and lower polarizing plates 10 and 20 has a configuration in which the polarizing plate 1 is disposed on the TAC base film 2. The polarizing plate polarizing layer 1 is made of, for example, stretched polyvinyl alcohol.

  In the illustrated azimuth coordinate system in which the horizontal direction of the liquid crystal display element is defined as 180 ° -0 ° (9 o'clock-3 o'clock), the absorption axis Fab in the polarizing layer 1 of the upper polarizing plate 10 is 135 ° azimuth, lower side The absorption axis Rab of the polarizing layer 1 of the polarizing plate 20 is arranged in the 45 ° azimuth. The orientation in which the in-plane slow axis SA1 of the first optical film 3 is disposed is 45 °.

  As described above, since the retardation Rth in the thickness direction of the first optical film can only be set to about 500 nm or less, in the liquid crystal display element according to the first conventional example, the retardation Δnd of the liquid crystal layer 5 is large. In this case, good viewing angle compensation cannot be obtained in the background portion and the non-display portion.

  FIG. 9B is a schematic diagram of a liquid crystal display element according to a second conventional example. For example, a single second optical film 7 which is a norbornene COP biaxially stretched film is disposed between the lower glass substrate 6 and the lower polarizing plate 20 of the vertical alignment liquid crystal cell 30. Is different. The orientation in which the in-plane slow axis SA2 of the second optical film 7 is disposed is 135 °. The first conventional example is a single-sided compensation liquid crystal display element, whereas the second conventional example is a double-sided compensation liquid crystal display element.

  In the liquid crystal display element according to the second conventional example, the thickness direction retardation of the optical film can be set to about 1000 nm at the maximum as the sum of the first and second optical films. However, a deep polar angle as viewed from the normal direction in the left-right direction (180 ° -0 ° direction) set to about 45 ° with respect to the absorption axes Fab, Rab of the upper and lower polarizing plates 10, 20 When observed from an angle, the light transmittance of the bright display portion becomes extremely low, and the display may not be visible at all.

  The inventor of the present application obtained the right and left azimuth viewing angle characteristics during bright display by simulation for the liquid crystal display elements according to the first and second conventional examples. LCDMASTER 6.16 manufactured by Shintech Co., Ltd. was used as the simulator. The same simulator was used in other simulations in this specification.

  In both the first and second conventional examples, the vertical alignment liquid crystal cell 30 has a pretilt angle of 89.9 ° with respect to the substrate surface, in which the central molecular alignment direction of the liquid crystal layer 5 is set to 6 o'clock (270 ° azimuth). Anti-parallel monodomain alignment and a liquid crystal material having a negative dielectric anisotropy Δε. The retardation Δnd of the liquid crystal layer 5 was about 430 nm in the first conventional example and about 445 nm in the second conventional example. As the upper and lower polarizing plates 10 and 20, SHC13U manufactured by Polatechno Co., Ltd. was adopted, the in-plane retardation of the TAC base film 2 was set to 3 nm, and the retardation in the thickness direction was set to 50 nm.

  As described above, the first and second optical films 3 and 7 are composed of norbornene COP biaxially stretched films. In the simulation, the in-plane retardation of the first optical film 3 in the first conventional example was 50 nm, and the retardation in the thickness direction was 300 nm. In the second conventional example, both the in-plane retardation of the first and second optical films 3 and 7 is 30 nm, and the retardation in the thickness direction is both 150 nm. Both the first and second conventional examples are the optimum optical film conditions in which the light transmittance when observed from the right azimuth polar angle of 50 ° when no voltage is applied is less than 0.03%.

  FIG. 10 is a graph showing the left-right azimuth viewing angle characteristics when the light transmittance during frontal observation is set to about 15%.

  The horizontal axis of the graph represents the horizontal observation angle in the unit “°”, and the vertical axis represents the light transmittance in the unit “%”. Curve a shows the viewing angle characteristic of the liquid crystal display element (single-sided compensation) according to the first conventional example during left-right observation, and curve b shows the viewing angle characteristic of the liquid crystal display element according to the second conventional example (double-sided compensation) during left-right observation. Show.

  It can be seen from the figure that the liquid crystal display element (single-sided compensation) according to the first conventional example has a higher light transmittance at an observation angle deeper than the polar angle of 50 °. On the other hand, the symmetry is better in the liquid crystal display element (double-sided compensation) according to the second conventional example.

  Note that when the inventors of the present invention actually manufactured the liquid crystal display elements according to the first and second conventional examples, in the second conventional example, there is a tendency that a color shift at a deep angle is noticeably observed, It turned out to be undesirable.

  When the liquid crystal display element is operated by multiplex driving, in order to obtain a larger display capacity, that is, a duty ratio, it is necessary that the steepness in electro-optical characteristics is good. In the case of a vertical alignment type liquid crystal display element, the steepness greatly affects the transmittance of the bright display portion, and thus is reflected in the display luminance.

  When it is desired to make the display capacity larger than the ¼ duty driving condition, the retardation Δnd of the liquid crystal layer is preferably larger than 300 nm, and more preferably larger than 360 nm. When it is desired to make the display capacity larger than the 1/16 duty driving condition, the retardation Δnd of the liquid crystal layer is preferably larger than 550 nm, and more preferably larger than 600 nm. When a display capacity exceeding 1/16 duty is required, it is possible to obtain good display performance even if the liquid crystal display elements according to the first and second conventional examples are configured by using generally available optical films. It is considered difficult.

Japanese Patent No. 2047880 Japanese Patent No. 3330574

  An object of the present invention is to provide a liquid crystal display element capable of realizing good display.

  According to one aspect of the present invention, a liquid crystal display element is provided with respect to a substrate having a retardation of 300 nm or more and 1200 nm or less sandwiched between the first and second transparent substrates and the first and second transparent substrates. Liquid crystal layer vertically or substantially vertically aligned, and first and second optical films having negative biaxial optical anisotropy disposed on the opposite side of the first transparent substrate from the liquid crystal layer; The first polarizing plate disposed on the opposite side of the first and second optical films to the first transparent substrate, and the first transparent plate on the opposite side of the liquid crystal layer of the second transparent substrate. And a second polarizing film disposed in crossed Nicols, wherein the second optical film is disposed between the first transparent substrate and the first optical film in the previous period, The in-plane slow axis of the first optical film is orthogonal to the absorption axis of the first polarizing plate. Arranged in such a way that the in-plane slow axis of the first optical film and the in-plane slow axis of the second optical film are orthogonal to each other, and the position of the in-plane orientation of the first optical film The phase difference is larger than the phase difference of the in-plane orientation of the second optical film.

  ADVANTAGE OF THE INVENTION According to this invention, the liquid crystal display element which can implement | achieve favorable display can be provided.

It is the schematic of the liquid crystal display element by an Example. It is a graph of the analysis result which shows Re1 as a parameter about Re2 dependence of the light transmittance when observing from right azimuth | direction polar angle 40 degrees and 50 degrees. It is a graph which shows the search result about the Rth dependence of Re1 when Re2 = 0 nm. From the search results shown in FIG. 2, Re2 is obtained by overlapping or intersecting the Re2 dependence curves of the background transmittance of 40 ° and 50 ° in the right direction under each Re1 condition, and Re2 is plotted on the horizontal axis and Re1 is plotted on the vertical axis. is there. FIG. 5 is a graph plotting the optimal relationship between the liquid crystal layer retardation Δnd and Re1 when Rth is 180 nm, 300 nm, and 440 nm using the relationship between Re1 and Re2 shown in FIG. 4. It is a graph which shows Re2 dependence of the background transmittance | permeability at the time of polar angle 40 degree observation at the time of changing Re1 and 50 degree polar angle. It is a graph which shows the Re2 dependence of the background transmittance | permeability at the time of the right azimuth | direction polar angle 40 degree observation and the polar angle 50 degree observation at the time of changing Rth2. It is the schematic of the liquid crystal display element by a modification. It is the schematic which shows the liquid crystal display element by a prior art example. It is a graph which shows the right-and-left azimuth viewing angle characteristic when the light transmittance at the time of front observation is set to about 15%.

  FIG. 1 is a schematic view of a liquid crystal display device according to an embodiment.

  Between the upper polarizing plate 10 and the lower polarizing plate 20 arranged substantially in crossed Nicols, a liquid crystal cell having a vertical alignment liquid crystal layer subjected to vertical or substantially vertical alignment treatment, for example, a monodomain vertical alignment liquid crystal cell 30 is arranged. Is done. The monodomain vertical alignment liquid crystal cell 30 includes an upper glass substrate (transparent substrate) 4, a lower glass substrate (transparent substrate) 6, and a monodomain vertical alignment liquid crystal layer 5 sandwiched between the substrates 4 and 6. Is done. Between the upper glass substrate 4 and the upper polarizing plate 10 of the vertical alignment liquid crystal cell 30, the first optical film 8 and the second optical film 9 are arranged in this order from the upper polarizing plate 10 side. As the optical films 8 and 9, for example, a stretched film of norbornene COP can be used.

  As the upper and lower polarizing plates 10 and 20, for example, SHC13U manufactured by Polatechno Co., Ltd. is used. Each of the upper and lower polarizing plates 10 and 20 has a configuration in which the polarizing plate 1 is disposed on the TAC base film 2. The polarizing plate polarizing layer 1 is made of, for example, stretched polyvinyl alcohol. In addition, although illustration was abbreviate | omitted, the TAC film used as a protective film is laminated | stacked on the outer surface of the liquid crystal display element at the upper and lower polarizing plates 10 and 20.

  The in-plane slow axis SA1 of the first optical film 8 disposed in the vicinity of the upper polarizing plate 10 is disposed substantially orthogonal to the absorption axis Fab of the upper polarizing plate 10. The in-plane slow axis SA2 of the second optical film 9 disposed between the first optical film 8 and the vertically aligned liquid crystal cell 30 is substantially orthogonal to the in-plane slow axis SA1 of the first optical film 8. Placed in.

  In the illustrated azimuth coordinate system in which the horizontal direction of the liquid crystal display element is defined as 180 ° -0 ° (9-3 o'clock), the absorption axis Fab of the upper polarizer 10 is 135 °, and the lower polarizer 20 The absorption axis Rab is 45 ° azimuth, the in-plane slow axis SA1 of the first optical film 8 is 45 ° azimuth, and the in-plane slow axis SA2 of the second optical film 9 is 135 ° azimuth.

  The vertically aligned liquid crystal layer 5 is formed using a liquid crystal material manufactured by Merck Co., Ltd., which exhibits properties of refractive index anisotropy Δn <0.1 and dielectric anisotropy Δε <−5.1, for example. An alignment film is formed on the surfaces of the upper and lower glass substrates 4 and 6 on the liquid crystal layer 5 side using, for example, an alignment film material SE1211 manufactured by Nissan Chemical Co., Ltd. The alignment film is subjected to an anti-parallel monodomain vertical alignment process that realizes a pretilt angle of approximately 90 °, for example, 89.9 °, with respect to the substrate surface. The liquid crystal layer central molecular orientation direction of the vertically aligned liquid crystal layer 5 is 6 o'clock (270 °).

  The upper and lower glass substrates 4 and 6 have transparent electrodes, such as ITO electrodes, for switching the display pattern of the liquid crystal display element by changing the alignment state of the liquid crystal molecules of the liquid crystal layer 5 inside the alignment film. Has been placed.

  The inventor of the present application conducted simulation analysis with various changes in the optical characteristics of the first and second optical films 8 and 9 in the liquid crystal display element according to the example, and investigated conditions for realizing good display.

  (I) First, in the case where negative biaxial films are used for both the first and second optical films 8 and 9, the viewing angle characteristics when no voltage is applied to the liquid crystal display element, that is, the viewing angle characteristics of the background portion of the display Was simulated.

  (I) First, the case where the retardations Rth1 and Rth2 in the thickness direction of the first and second optical films 8 and 9 are equal (Rth1 = Rth2) was examined. For each of the cases where Rth1 (= Rth2) is 90 nm, 180 nm, 300 nm, and 400 nm, the dependency of the background light transmittance upon observation of the right polar angle of 40 ° and 50 ° on the liquid crystal layer retardation Δnd was analyzed. The analysis is performed for various conditions of the in-plane retardations Re1 and Re2 of the first and second optical films 8 and 9, and the light transmittance of the background part at the time of observation at right angles of 40 ° and 50 ° under each condition. We searched for Δnd that minimizes the value and the conditions under which both transmittances are equal.

  FIGS. 2A to 2C are graphs of analysis results showing Re2 dependence of light transmittance when observed from the right azimuth polar angles of 40 ° and 50 °, with Re1 as a parameter. The horizontal axes of the graphs of FIGS. 2A to 2C all represent Re2 in the unit “nm”. The vertical axis represents the light transmittance when observed from the right azimuth polar angles of 40 ° and 50 ° in the unit “%”.

  The graphs of FIGS. 2A, 2B, and 2C are analysis results when Rth1 (= Rth2) is 180 nm, 300 nm, and 440 nm, respectively, in order. Although Δnd changes corresponding to the values of Re1, Re2, and Rth, the transmittance is set to a value that is almost the lowest under any condition.

  In FIG. 2A, the relationship between Re2 and light transmittance when Re1 = 80 nm and polar angle 40 ° is represented by curve a, and the relationship between both when Re1 = 80 nm and polar angle 50 ° is represented by curve b. The relationship between Re1 = 100 nm and polar angle 40 ° is curve c, and when Re1 = 100 nm and polar angle 50 °, the relationship is curve d, Re1 = 140 nm and polar angle 40 °. The relationship between the two is the curve e, the relationship between Re1 = 140 nm and the polar angle of 50 ° is the curve f, the relationship between Re1 = 180 nm and the polar angle of 40 ° is the curve g, Re1 = 180 nm, The relationship between the two at a polar angle of 50 ° is indicated by a curve h.

  In FIG. 2B, the relationship between Re1 = 70 nm, polar angle 40 °, and polar angle 50 ° is shown by curves i and j in order, Re1 = 100 nm, polar angle 40 °, and polar angle 50. The relationship between the two at the time of ° is shown by curves k and l in order, and the relationship at the time of Re1 = 180 nm, polar angle 40 ° and polar angle 50 ° is shown by curves m and n in order.

  In FIG. 2C, the relationship between Re1 = 45 nm, polar angle 40 °, and polar angle 50 ° is shown in the order of curves o and p, with Re1 = 70 nm, polar angle 40 °, and polar angle 50. The relationship between the two at the time of ° is sequentially shown by curves q and r, and the relationship at the time of Re1 = 100 nm, polar angle 40 ° and polar angle 50 ° is shown by curves s and t in order.

  Curves a to t in any of the graphs of FIGS. 2A to 2C are downwardly convex quadratic function curves in which a specific Re2 has the lowest transmittance. Among them, when Rth is smaller and Re1 is smaller, there is a tendency that the minimum value at 40 ° observation and 50 ° observation can be obtained at the same Re2. On the other hand, as Rth and Re1 increase, a difference occurs in Re2 from which these minimum values are obtained, and the difference tends to increase. This result is considered to indicate that the smaller the Rth and Re1, the smaller the background light leakage at a wide observation angle. On the contrary, when Rth and Re1 are increased, it can be confirmed that the smaller the observation angle (40 °), the greater the tendency of the light passing through, and the narrower the viewing angle characteristics.

  Here, from the observation results of FIGS. 2A to 2C, the Rth dependency of Re1 when Re2 = 0 nm was derived.

  FIG. 3A is a graph showing the search results for the Rth dependence of Re1 when Re2 = 0 nm. The observation angle was considered only at 50 °, and exploration was performed with respect to the conditions where the background transmittance was 0.05% or less and 0.1% or less. In FIG. 3A, the shaded area indicates the background transmittance of 0.05% or less, and the shaded area indicates the area of 0.1%. It has been found that the boundary lines of the respective regions have an inversely proportional relationship represented by Re1 = A + B / Rth.

It has been found that when the background transmittance is 0.05% or less, the least square fitting can be performed by the following equation (1). However, Re1 / 2 <Rth1 = Rht2 ≦ 500 nm.
29.81 + 5466.7 / Rth ≦ Re1 ≦ 18.427 + 4278.3 / Rth (1)
Further, it was found that when the background transmittance is 0.1% or less, the least square fitting can be performed by the following equation (2). However, Re1 / 2 <Rth1 = Rht2 ≦ 500 nm.
31.389 + 6440.4 / Rth≤Re1≤20.975 + 2114.6 / Rth ... Formula (2)
Further, in the liquid crystal display element structure shown in FIG. 1, the TAC film 2 constituting the polarizing plate 10 was removed, and the structure in which the first optical film 8 was directly adhered to the polarizing layer 1 of the polarizing plate was similarly investigated. FIG. 3B shows the search results. As in FIG. 3A, the shaded area indicates the background transmittance of 0.05% or less, and the hatched area indicates the area of 0.1%. When the TAC film 2 is not present, Re1 tends to increase at the same Rth. Similar to the case shown in FIG. 3A, the boundary lines of the respective regions are in an inversely proportional relationship and can be fitted.

When the background transmittance is 0.05% or less, the least square fitting can be performed by the following equation (3). However, 90 nm ≦ Rth1 = Rth2 ≦ 500 nm.
17.647 + 7620.7 / Rth≤Re1≤17.412 + 9117.2 / Rth (3)
Further, it was found that when the background transmittance is 0.1% or less, the least square fitting can be performed by the following equation (4). However, 90 nm ≦ Rth1 = Rth2 ≦ 500 nm.
26.115 + 11079 / Rth ≤ Re1 ≤ 25.88 + 12575 / Rth (4)
In the embodiment of the present invention, the liquid crystal display element under the conditions of Re1> 0 and RE2> 0 is described, which is different from the range of Re1 shown in FIGS. At least, Re1 needs to be larger than the lower limits shown by the above formulas (1) to (4). Therefore, when the background transmittance is 0.05% or less under the condition where the TAC film is present in the polarizing plate shown in FIG. When it is desired to make it 1% or less, it is necessary that Re1> 31.389 + 6440.4 / Rth. In the case where the background transmittance is 0.05% or less under the condition that the TAC film is not present on the polarizing plate shown in FIG. When it is desired to set the ratio to 1% or less, it is necessary that Re1> 26.115 + 111079 / Rth.

  That is, in the configuration in which the TAC film is present in the polarizing plate shown in FIG. 3A, if the in-plane retardation of the first optical film is Re1 and the thickness direction retardation is Rth, Re1> 31.389 + 6440.4. / Rth, preferably Re1> 29.81 + 5466.7 / Rth, and more preferably 40 nm ≦ Re1 ≦ 180 nm.

  In the configuration in which the TAC film is not present in the polarizing plate shown in FIG. 3B, when the in-plane retardation of the first optical film is Re1 and the thickness direction retardation is Rth, Re1> 26.115 + 111079 / Rth. It is preferable that Re1> 17.647 + 7620.7 / Rth and 50 nm ≦ Re1 ≦ 180 nm.

  FIG. 4 shows Re2 on the horizontal axis, Re2 on the horizontal axis, and Re1 on the vertical axis, from the search results shown in FIG. This is a plotted graph. FIG. 4A shows a case where there is a TAC film constituting the polarizing plate 10, and FIG. 4B shows a case where there is no TAC film constituting the polarizing plate 10. In the figure, Rth = 180, 300, and 440 nm are shown by straight lines a, b, and c, respectively.

  Linear least square fitting was possible in any plot. Assuming that Re1 when Re2 = 0 is Re0, the relationship is not Re2 = Re1-Re0, and it can be seen that the slope varies depending on Rth. That is, the in-plane retardation of the first optical film is not offset by the in-plane retardation of the second optical film whose slow axis is arranged orthogonal to that of the first optical film.

  As Rth increases, the slopes of the straight lines a, b, and c shown in FIGS. 4A and 4B tend to be gentle, but the straight line slopes are all 1 and Rth is 180 to 440 nm. In the range, a minimum of about 1.2 and a maximum of about 2.3, a change of a quadratic function is seen with respect to the magnitude of Rth. That is, assuming that the intercept is A, 1.2 ≦ B ≦ 2.3 in the formula of Re1 = A + B × Re2. Note that the intercept A is effective within the range of the mathematical formula obtained in FIG. 3 with the background transmittance range being 0.05% or 0.1%, and both FIGS. 4A and 4B are within the range. You can see that it exists.

  That is, in the configuration in which the TAC film is present in the polarizing plate, when the in-plane retardation of the first optical film is Re1, the thickness direction retardation is Rth, and the in-plane retardation of the second optical film is Re2, Re1 = A + B × Re2, A = 31.389 + 6440.4 / Rth, more preferably A = 29.81 + 5466.7 / Rth, and 1 ≦ B ≦ 2.3, more preferably 1.2 ≦ B ≦ 2.3 It is further preferable to have

  In the configuration in which the TAC film does not exist in the polarizing plate, when the in-plane retardation of the first optical film is Re1, the thickness direction retardation is Rth, and the in-plane retardation of the second optical film is Re2, Re1 = A + B × Re2, A = 26.115 + 111079 / Rth, more preferably A = 1.647 + 7620.7 / Rth, and 1 ≦ B ≦ 2.3, more preferably 1.2 ≦ B ≦ 2.3. More preferably.

  FIG. 5 is a graph plotting the optimal relationship between the liquid crystal layer retardation Δnd and Re1 when Rth is 180 nm, 300 nm, and 440 nm using the relationship between Re1 and Re2 shown in FIG. FIG. 5A shows a case where there is a TAC film constituting the polarizing plate 10, and FIG. 5B shows a case where there is no TAC film constituting the polarizing plate 10. In the figure, Rth = 180, 300, and 440 nm are shown by straight lines a, b, and c, respectively. Further, Rth = 90 in FIG. 5A is indicated by a straight line d.

  Under each Rth condition, Δnd tends to decrease almost linearly as Re1 increases. Further, it was found that the inclination tends to increase as Rth increases and does not depend on the presence or absence of the TAC film.

  When each plot data was subjected to least square method curve fitting using the model equation Δnd = A + B × Re1, in FIG. 5A, fitting was possible by the following equations (5) to (7) at each Rth.

When Rth = 180 nm (Rth1 + Rth2 = 360 nm),
Δnd = 600−0.75 × Re1 Formula (5)
When Rth = 300 nm (Rth1 + Rth2 = 600 nm)
Δnd = 885.01−1.0743 × Re1 Equation (6)
When Rth = 440 nm (Rth1 + Rth2 = 880 nm),
Δnd = 12033-1.3581 × Re1 (7)
Moreover, it turned out that all the plots can be fitted by the following formula | equation (8).
Δnd = (185.18 + 23179 × Rth) − (0.34619 + 0.0023303 × Rth) × Re1 = (185.18 + 23179 × ((Rth1 + Rth2) / 2)) − (0.34619 + 0.0023303 × ((Rth1 + Rth2) / 2)) × Re1… Formula (8)
On the other hand, in FIG. 5B, fitting was possible by the following formulas (9) to (11) at each Rth. Note that the intercept and the inclination are both smaller compared to the case with the TAC film (FIG. 5A).

When Rth = 180 nm (Rth1 + Rth2 = 360 nm),
Δnd = 517.5−0.375 × Re1 Equation (9)
When Rth = 300 nm (Rth1 + Rth2 = 600 nm)
Δnd = 812.03−0.64665 × Re1 Formula (10)
When Rth = 440 nm (Rth1 + Rth2 = 880 nm),
Δnd = 1119.1−0.82418 × Re1 Equation (11)
Moreover, it turned out that all the plots can be fitted by the following formula | equation (12).
Δnd = (107.65 + 2.3105 × Rth) − (0.089358 + 0.001715 × Rth) × Re1 = (107.65 + 2.3105 × ((Rth1 + Rth2) / 2)) − (0.089358 + 0.001715 × ((Rth1 + Rth2) / 2) ) X Re1 Formula (12)
The above functional formulas (5) to (12) of Δnd are combinations in which Re1, Re2, and Rth are optimal, and the background transmittances in the right direction of 40 ° or 50 ° are overlapped, that is, are equal. In an actual liquid crystal display element, the transmittance is in an acceptable range in appearance, and therefore at least ± 50 nm, preferably ± 100 nm, is allowed from Δnd according to the above formulas (5) to (12).

  (Ii) Next, the inventor of the present application also performed a simulation analysis when the thickness direction retardations Rth1 and Rth2 of the first and second optical films 8 and 9 were different. When the in-plane retardation Re1 of the first optical film 8 is changed to 120 nm, 140 nm, and 180 nm, Rth1 is fixed to 180 nm, and the thickness direction retardation Rth2 of the second optical film 9 is fixed to 440 nm. Then, the Re2 (in-plane retardation of the second optical film 9) dependency of the light transmittance of the background portion at the time of observation of the right polar angle of 40 ° and 50 ° was calculated. In the simulation, the retardation Δnd of the liquid crystal layer was appropriately changed so that the background light transmittance was minimized.

  FIG. 6A is a graph showing calculation results. The horizontal axis of the graph represents Re2 in units of “nm”, and the vertical axis represents light transmittance in units of “%” when observed from the right azimuth polar angles of 40 ° and 50 °.

  Plots are shown for each Re1 condition. A solid line indicates a right azimuth polar angle of 40 ° observation, and a broken line indicates a right azimuth polar angle of 50 ° observation. Specifically, the curves a and b show the Re2 dependence of the background transmittance when the polar angle is 40 ° and when the polar angle is 50 ° when Re1 = 120 nm. Curves c and d are respectively observed at a polar angle of 40 ° when Re1 = 140 nm and observed at a polar angle of 50 °. Curves e and f are respectively observed at a polar angle of 40 ° when Re1 = 180 nm. The Re2 dependency of the background transmittance at the time of observation and at a polar angle of 50 ° is shown.

  As Re1 increases, (1) the increase in Re2 at which the background transmittance is minimum, (2) the transmittance increases at Re2 where the minimum transmittance is obtained, and (3) at the time of observation at the right polar angle 40 ° An increase in the difference in Re2 is observed, which gives the minimum transmittance when observing the right polar angle of 50 °. Re1 when Re2 = 0 shown in FIG. 3A is about 80 nm when Rth1 is 180 nm, and relatively good viewing angle characteristics when Re1 is from a larger value to about 180 nm. Can be obtained.

  FIG. 6A shows the case where Rth1 <Rth2 is satisfied, but analysis was also performed for the case where Rth1> Rth2 which is the reverse relationship. The in-plane retardation Re1 of the first optical film 8 is changed to 60 nm, 80 nm, 120 nm, 140 nm, and 180 nm, Rth1 is fixed to 440 nm, and the thickness direction retardation Rth2 of the second optical film 9 is 180 nm. In the case of fixing, the Re2 (in-plane retardation of the second optical film 9) dependence of the background light transmittance at the time of observation at right polar angles of 40 ° and 50 ° was calculated.

  FIG. 6B is a graph showing the calculation results. The horizontal axis of the graph represents Re2 in units of “nm”, and the vertical axis represents light transmittance in units of “%” when observed from the right azimuth polar angles of 40 ° and 50 °.

  Plots are shown for each Re1 condition. A solid line indicates a right azimuth polar angle of 40 ° observation, and a broken line indicates a right azimuth polar angle of 50 ° observation. Specifically, the curves a and b show the Re2 dependence of the background transmittance when the polar angle is 40 ° and when the polar angle is 50 ° when Re1 = 60 nm. Curves c and d are respectively observed at a polar angle of 40 ° when Re1 = 80 nm and at a polar angle of 50 °. Curves e and f are respectively observed at a polar angle of 40 ° when Re1 = 120 nm. Curves g and h at the time of observation and polar angle 50 ° are respectively curves i and j at the time of observation of polar angle 40 ° and polar angle 50 ° when Re1 = 140 nm are respectively Re1 = 180 nm. The Re2 dependence of the background transmittance when the polar angle is 40 ° and when the polar angle is 50 ° is shown.

  As in the case of the relationship of Rth1 <Rth2 shown in FIG. 6A, as Re1 increases, (1) the increase in Re2 at which the background transmittance is minimized, and (2) the minimum transmittance is obtained. The transmittance increases in Re2, and (3) an increase in the difference in Re2 is obtained in which the minimum transmittance is obtained when observing the right azimuth polar angle of 40 ° and the right azimuth polar angle of 50 °. There is a tendency that the increase in the value of Re1 for the background transmittance at the polar angle of 40 ° observation is small and the increase in the value of the background transmittance for Re1 at the polar angle of 50 ° is large. That is, compared to the case where Rth1 <Rth2 is satisfied, there is a difference in the change in the background transmittance particularly during deep polar angle observation. From FIG. 3A, when Rth = 440 nm, Re1 is considered to be about 50 nm when Re2 = 0 nm. Therefore, both Re1 and Re2 are smaller values than when Rth1 <Rth2. Can be taken.

  From the above analysis, it was found that good viewing angle characteristics can be realized even when the values of Rth1 and Rth2 are different.

  In the above analysis, Re2 was optimized with Rth2 fixed. However, when the first optical film is fixed and Rth2 of the second optical film is changed, good viewing angle characteristics can be realized. Confirmed whether or not. Re2 and Rth2 change with respect to the two conditions of Re1 = 120 nm and Rth180 nm (FIG. 6A) and Re1 = 80 nm and Rth1 = 440 nm (FIG. 6B) of the first optical film described above. As a result, it was calculated how the background transmittance changes when observing the right polar angle of 40 ° and 50 °.

  FIG. 7A is a graph showing calculation results. The horizontal axis of the graph represents Re2 in units of “nm”, and the vertical axis represents light transmittance in units of “%” when observed from the right azimuth polar angles of 40 ° and 50 °. When Re1 = 120 nm and Rth = 180 nm, when Rth2 is changed to 90 nm, 300 nm, and 440 nm, the Re2 dependence of the background transmittance at the time of right-angle polar angle 40 ° observation and polar angle 50 ° observation Show.

  In the plots corresponding to each Rth2, the solid line indicates the right azimuth polar angle of 40 ° observation, and the broken line indicates the right azimuth polar angle of 50 ° observation. Specifically, the curves a and b show the Re2 dependence of the background transmittance when the polar angle is 40 ° and when the polar angle is 50 ° when Rth2 = 90 nm. Curves c and d are the polar angle 40 ° observation when Rth2 = 300 nm and the polar angle 50 ° observation when the polar angle 50 ° observation, respectively. Curves e and f are the polar angle 40 ° observation when Rth2 = 440 nm, respectively. The Re2 dependency of the background transmittance at the time of observation and at a polar angle of 50 ° is shown.

  As Rth2 increases, there is a difference in the Re2 dependency curve of the background transmittance during polar angle 40 ° observation and polar angle 50 ° observation, but during polar angle 40 ° observation and polar angle 50 ° observation. Since the intersection of the Re2 dependence curves of the background transmittance of 30 to 35 nm shows almost no difference, it is considered that even if Rth2 changes, even if Re2 is fixed, almost good viewing angle characteristics can be realized.

  FIG. 7B shows a background when observing a right-angle polar angle of 40 ° and a polar angle of 50 ° when Rth2 is changed to 90 nm, 180 nm, and 300 nm when Re1 = 80 nm and Rth = 440 nm. The Re2 dependence of transmittance is shown. The horizontal axis of the graph represents Re2 in units of “nm”, and the vertical axis represents light transmittance in units of “%” when observed from the right azimuth polar angles of 40 ° and 50 °.

  In the plots corresponding to each Rth2, the solid line indicates the right azimuth polar angle of 40 ° observation, and the broken line indicates the right azimuth polar angle of 50 ° observation. Specifically, the curves a and b show the Re2 dependence of the background transmittance when the polar angle is 40 ° and when the polar angle is 50 ° when Rth2 = 90 nm. Curves c and d are the polar angle 40 ° observation when Rth2 = 180 nm and the polar angle 50 ° observation when the polar angle 50 ° observation, respectively. Curves e and f are the polar angle 40 ° observation when Rth2 = 300 nm, respectively. The Re2 dependency of the background transmittance at the time of observation and at a polar angle of 50 ° is shown.

  Similar to the case shown in FIG. 7A, as Rth2 increases, a difference occurs in the Re2 dependency curve of the background transmittance at the time of polar angle 40 ° observation and at the polar angle 50 ° observation. The crossing point of the Re2 dependence curve of the background transmittance at the time of observation at an angle of 40 ° and an observation at a polar angle of 50 ° is almost 30 to 35 nm, so even if Rth2 changes, even if Re2 is fixed, it is almost It is considered that good viewing angle characteristics can be realized. Therefore, it is considered that the optimum parameter setting method at the time of Rth1 = Rth2 examined in more detail can be applied as it is.

  From the above analysis results, even when Rth1 and Rth2 are not equal, it is possible to achieve good viewing angle characteristics by setting appropriate in-plane retardation, thickness direction retardation, and retardation Δnd of the liquid crystal layer. is there.

  (Iii) FIG. 8 shows a schematic diagram of a liquid crystal display element according to a modification. The liquid crystal display element according to the modification is different from the liquid crystal display element according to the embodiment in that a negative C plate 11 is disposed between the upper glass substrate 4 and the second optical film 9. In the liquid crystal display element shown in FIG. 5, one negative C plate 11 is disposed, but a plurality of negative C plates can also be disposed.

  The liquid crystal display element according to the modified example can achieve good viewing angle characteristics even when the retardation Δnd of the liquid crystal layer 5 is larger than 750 nm, for example. However, if Δnd is increased, light leakage from a deep polar angle is increased, and the in-plane uniformity of the Δnd setting tends to become severe. When the present inventor manufactured an actual machine, it was confirmed that good display was possible with Δnd up to about 1200 nm. It should be noted that the thickness direction retardation of the single or plural C plates is changed to the calculation formula (Mathematical Expressions (5) to (12)) of the optimum Δnd when the C plate is not inserted. It can be applied by adding to the direction phase difference Rth2.

  In the above-described embodiments, the first and second optical films have been described using negative biaxial optical anisotropy. However, positive uniaxial optical anisotropy, that is, nx> ny = nz A plate with nz = 1 is also applicable. In the case of the A plate, the thickness direction retardation Rth with respect to the in-plane retardation Re is represented by Rth = Re / 2. Although it confirmed by simulation analysis, there is no difference from the case of the negative biaxial optical anisotropy examined in the said Example. Therefore, the relationship by the mathematical formulas of Re1, Re2, Rth1, Rth2, and Δnd can be handled in the same manner.

  Furthermore, only the first optical film has a negative A plate having nx> ny = nz, nz = −1, and positive biaxial optical anisotropy indicating nx> ny = nz, 1 ≦ nz <−1. Even if a thing is used, it can be handled equally.

  As mentioned above, although this invention was demonstrated along the Example and the modification, this invention is not limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

  It can be generally used for liquid crystal display elements. For example, it can be suitably used for a liquid crystal display element capable of both segment display, dot matrix display, and these two displays. Further, it can be suitably used for a TFT-driven liquid crystal display element and a multiplex-driven liquid crystal display element having a display capacity of, for example, ¼ duty or more.

DESCRIPTION OF SYMBOLS 1 Polarizing plate polarization layer 2 TAC base film 3 First optical film 4 Upper glass substrate 5 Vertical alignment liquid crystal layer 6 Lower glass substrate 7 Second optical film 8 First optical film 9 Second optical film 10 Upper polarization Plate 11 Negative C plate 20 Lower polarizing plate 30 Vertical alignment liquid crystal cell Fab Upper polarizing plate polarizing layer absorption axis Rab Lower polarizing plate polarizing layer absorption axis SA1 In-plane slow axis SA2 of the first optical film Second optical film In-plane slow axis

Claims (7)

First and second transparent substrates;
A liquid crystal layer sandwiched between the first and second transparent substrates and having a retardation that is perpendicular or substantially perpendicular to a substrate having a retardation of 300 nm or more and 1200 nm or less;
First and second optical films having negative biaxial optical anisotropy disposed on a side opposite to the liquid crystal layer of the first transparent substrate;
A first polarizing plate disposed on the opposite side of the first and second optical films from the first transparent substrate;
The second transparent substrate has a second polarizing plate disposed on the opposite side of the liquid crystal layer from the first polarizing plate and crossed Nicols,
The second optical film is disposed between the first transparent substrate and the first optical film,
The in-plane slow axis of the first optical film and the absorption axis of the first polarizing plate are arranged to be orthogonal to each other,
The in-plane slow axis of the first optical film and the in-plane slow axis of the second optical film are arranged to be orthogonal to each other,
A liquid crystal display element in which an in-plane phase difference of the first optical film is larger than an in-plane phase difference of the second optical film.   The liquid crystal display element according to claim 1, wherein Re1> 31.389 + 6440.4 / Rth, where Re1 is an in-plane retardation of the first optical film and Rth1 is a thickness direction retardation.   The in-plane retardation of the second optical film is Re2, and Re1 = A + B × Re2, A = 26.115 + 6440.4 / Rth1, and 1 ≦ B ≦ 2.3. The liquid crystal display device described.   The thickness direction retardation Rth1, Rth2 of the first and second optical films is larger than a half value of each of the in-plane retardations Re1, Re2, and is 550 nm or less. The liquid crystal display element as described. When the retardation of the liquid crystal layer is Δnd, the liquid crystal layer is
Δnd = (185.18 + 23179 × Rth) − (0.34619 + 0.0023303 × Rth) × RE1 = (185.18 + 23179 × ((Rth1 + Rth2) / 2)) − (0.34619 + 0.0023303 × ((Rth1 + Rth2) / 2) 5. The liquid crystal display element according to any one of claims 1 to 4, which is in a range of [Delta] nd ± 100 nm at xRe1.   The liquid crystal display element according to claim 1, wherein one or both of the first and second optical films is an A plate.   The liquid crystal display element according to claim 1, wherein the first optical film is a negative A plate or a substance having positive biaxial optical anisotropy.

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