JP2014215433A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new visual angle compensation technique for a liquid crystal display element having a vertical orientation liquid crystal cell in which a retardation Δnd of the liquid crystal layer is 600 nm or more.SOLUTION: The liquid crystal display element has: a vertical orientation liquid crystal cell disposed between a first and a second polarizers disposed in cross-nicol alignment, a negative biaxial film disposed between the first polarizer and the liquid crystal cell, and a first and a second C plates disposed between the biaxial film and the liquid crystal cell and between the liquid crystal cell and the second polarizer, a retardation Δnd of a liquid crystal layer being 600 nm or more, an in-plane phase difference Re of the biaxial film being 40 nm≤Re≤120 nm, thickness direction retardations Rth1-Rth3 of the biaxial film and the first and second C plates being 50 nm≤Rth1≤500 nm, (Δnd-70)-Rth1-Rth3≤Rth2≤(Δnd-270)-Rth1-Rth3, 73 nm≤Rth3≤-107.67+0.34609Δnd, respectively.

Description

  The present invention relates to a liquid crystal display element.

  As a display device, a display device having a very low display brightness of a background display portion or a dark display portion is demanded. Conventionally, a fluorescent display tube display has been widely used, but a glass substrate used for the display itself. However, there is a problem that the power supply for driving is special. A liquid crystal display device can be mentioned as a device that can reduce the weight of the display device and can use an in-vehicle power supply as it is. Conventionally, contrast in front observation and right and left observation has been insufficient.

  Note that in this specification, a liquid crystal display device refers to a display device that includes a liquid crystal display element that displays information, a backlight that includes a light-emitting light source, a drive circuit that performs operation control thereof, and a control circuit. Recently, a normally black liquid crystal display element has been developed and used as an information display device, which uses an inorganic LED as the light source of the backlight to make the emission wavelength substantially monochromatic, thereby dramatically improving the contrast only at that wavelength. ing.

  As a liquid crystal display element that realizes a good normally black display regardless of the emission wavelength of the backlight, the liquid crystal molecule orientation in the liquid crystal layer disposed between the two upper and lower glass substrates is perpendicular or substantially perpendicular to the substrate There is an element in which a “vertical alignment mode” (hereinafter referred to as VA mode) liquid crystal cell that is aligned in the direction is arranged between substantially crossed Nicols polarizing plates. When observed from the normal direction of the glass substrate, the optical characteristics are almost the same as those of the crossed Nicols polarizing plate, the transmittance is very low, and a high contrast can be realized relatively easily.

  Furthermore, as shown in Patent Document 1, a viewing angle compensation plate having negative uniaxial optical anisotropy or negative biaxial optical anisotropy is inserted into one or both of the upper and lower polarizing plates and the upper and lower glass substrates. Thus, even when the liquid crystal display device is observed obliquely from the left and right with respect to the normal line, it is possible to realize a good display state in which the increase in transmittance is small and the contrast is relatively difficult to decrease. Regarding this viewing angle compensation method, Patent Document 2 discloses particularly effective conditions regarding the in-plane retardation and in-plane slow axis arrangement of a viewing angle compensation plate having negative biaxial optical anisotropy (hereinafter referred to as a negative biaxial film). Is shown in

  Also, a method for realizing a good viewing angle characteristic by combining a substantially ½ wavelength plate having biaxial optical anisotropy and a viewing angle compensation plate having negative uniaxial optical anisotropy (hereinafter referred to as C plate) is patented. It is shown in Reference 3. However, since this method needs to realize a phase difference of about ½ wavelength regardless of the direction of the wave plate itself as a substantially ½ wavelength plate, in actuality, there is a positive biaxial optical anisotropy. It is necessary and very difficult to realize. Therefore, Patent Document 4 discloses a method of combining a negative biaxial film and a C plate, which are considered to be relatively easy to manufacture. However, according to Patent Document 4, the in-plane retardation of the biaxial film is 190 nm or less, the retardation in the liquid crystal layer of the applied liquid crystal cell (Δnd when the birefringence of the liquid crystal material is Δn, and the thickness of the liquid crystal layer is d) Is limited to 200 nm to 500 nm.

  When the VA mode liquid crystal display element is operated at a duty of 1/64 or more by multiplex driving, the retardation Δnd in the liquid crystal layer is preferably at least larger than 550 nm, and more preferably larger than 800 nm. The reason for this is that unless the steepness in the electro-optic characteristics is made as good as possible, it is difficult to maintain both high contrast characteristics, which is a feature of the VA mode, and transmittance at the time of on-voltage application when the duty is high. It is to become.

  As described above, when Δnd is 500 nm or less, the viewing angle characteristics can be improved by the above method. However, in the case of Δnd larger than that, Patent Document 5 and Patent Document 6 show viewing angle compensation methods for realizing good viewing angle characteristics. .

  In Patent Document 5 (see FIG. 2), a VA mode liquid crystal cell is disposed between a front-side polarizing plate and a back-side polarizing plate arranged in crossed Nicols, and a negative biaxial film is disposed between the front-side polarizing plate and the VA mode liquid crystal cell. A liquid crystal display device is disclosed in which an in-plane slow axis is arranged to be orthogonal to the absorption axis of the front polarizing plate, and a C plate is arranged between the back polarizing plate and the VA mode liquid crystal cell.

  In Patent Document 6 (see FIG. 3), a VA mode liquid crystal cell is disposed between a front-side polarizing plate and a back-side polarizing plate arranged in crossed Nicols, and a negative biaxial film and a C plate are disposed between the front-side polarizing plate and the VA mode liquid crystal cell. However, the former discloses a liquid crystal display device which is disposed so as to be close to the front-side polarizing plate and the in-plane slow axis thereof is orthogonal to the absorption axis of the front-side polarizing plate.

  For a film-shaped optical compensator, when the in-plane refractive index is nx for the slow axis direction, ny for the fast axis direction, nz for the refractive index in the thickness direction, and d for the thickness, the negative biaxial film is , Nx> ny ≧ nz, the C compensator is defined as an optical compensator having a relationship of nx≈ny> nz. The in-plane retardation Re is defined by Re = (nx−ny) × d, and the thickness direction retardation Rth is defined by Rth = ((nx + ny) / 2−nz) × d.

  Resin films distributed in the market as negative biaxial films include those obtained by stretching a raw film having a thickness of about 0.2 mm or less made of norbornene-based cyclic olefin (hereinafter COP) in a biaxial direction. These films are considered difficult to achieve uniformity of optical parameters in the film unless the in-plane retardation Re is 0 <Re ≦ 300 nm and the thickness direction retardation Rth is 0 <Rth ≦ 500 nm.

  COP or triacetyl cellulose (hereinafter referred to as TAC) is used as a material for a resin film distributed as a C plate on the market. Since any film is uniaxially or biaxially stretched, the in-plane retardation Re is not completely zero but is often 7 nm or less. That is, nx≈ny> nz. If the thickness direction retardation Rth is not about 250 nm at the maximum, the in-plane Re and the slow axis uniformity cannot be ensured.

  When the maximum Rth = 500 nm of the negative biaxial film and the maximum Rth = 250 nm of the C plate are applied to the techniques described in Patent Document 5 and Patent Document 6, the total Rth of the viewing angle compensator is TAC which is a protective film for the back and front polarizing plates. When Rth = 50 nm of the film is added, it becomes about 850 nm. At this time, Δnd of the VA mode liquid crystal cell in the liquid crystal display device in which a good background (when no voltage is applied) viewing angle characteristic is obtained is about 750 nm to 950 nm. In combination with a VA mode liquid crystal display element having a Δnd higher than this, Patent Document 5 shows that it is effective to insert a plurality of C plates between the back-side polarizing plate and the liquid crystal cell. On the other hand, Patent Document 6 shows that it is effective to insert a C plate between the already arranged C plate and the VA mode liquid crystal cell.

Japanese Patent No. 2047880 Japanese Patent No. 3330574 Japanese Patent No. 3299190 Japanese Patent No. 3863446 Japanese Patent No. 4894036 Japanese Patent No. 4873553

  An object of the present invention is to provide a novel viewing angle compensation technique for a liquid crystal display element having a vertically aligned liquid crystal cell in which the retardation Δnd of the liquid crystal layer is 600 nm or more.

According to one aspect of the present invention,
A first polarizing plate and a second polarizing plate arranged in crossed Nicols,
A vertically aligned liquid crystal cell disposed between the first polarizing plate and the second polarizing plate;
It has optical anisotropy of nx> ny ≧ nz, and an in-plane slow axis is substantially orthogonal to the absorption axis of the first polarizing plate between the first polarizing plate and the vertically aligned liquid crystal cell. A first optical film arranged to
a second optical film having an optical anisotropy of nx≈ny> nz and disposed between the first optical film and the vertically aligned liquid crystal cell;
a third optical film having an optical anisotropy of nx≈ny> nz and disposed between the vertical alignment liquid crystal cell and the second polarizing plate;
The vertical alignment liquid crystal cell is
The retardation Δnd of the liquid crystal layer is 600 nm or more,
The first optical film is
In-plane retardation Re1 is 40 nm ≦ Re1 ≦ 120 nm,
Thickness direction retardation Rth1 is 50 nm ≦ Rth1 ≦ 500 nm,
The second optical film is
The thickness direction retardation Rth2 is (Δnd−70) −Rth1−Rth3 ≦ Rth2 ≦ (Δnd−270) −Rth1−Rth3,
The third optical film is
The thickness direction retardation Rth3 is 73 nm ≦ Rth3 ≦ −107.67 + 0.334609Δnd.
A liquid crystal display element is provided.

  A color shift accompanying a change in viewing angle is suppressed.

FIG. 1 is a schematic perspective view showing a panel structure of a liquid crystal display device according to an embodiment. FIG. 2 is a schematic perspective view showing the panel structure of the liquid crystal display element according to the first comparative example. FIG. 3 is a schematic perspective view showing a panel structure of a liquid crystal display element according to a second comparative example. FIG. 4a shows the left-right azimuth viewing angle characteristics when the transmittance during frontal observation is set to 7%, and FIG. 4b shows the left where chromaticity x and y are 0.35 or less when the transmittance is used as a parameter. The dependence of the maximum azimuth polar angle observation angle on the thickness direction retardation Rth3 of the second C plate is shown. FIG. 4 c shows the dependence of the maximum right azimuth polar angle at which the chromaticity x, y is 0.35 or less on the transmittance as a parameter in the thickness direction phase difference Rth3 of the second C plate, FIG. 4d shows the thickness direction position of the second C plate when the viewing angle range is the sum of polar angle observation angle ranges in which x and y are 0.35 or less in the left-right viewing angle characteristics of FIGS. 4b and 4c. The phase difference Rth3 dependency is shown. FIG. 5a shows the dependency of the maximum polar angle observation angle at which the chromaticity x, y in the left azimuth is 0.35 or less on the thickness direction phase difference Rth3 of the second C plate, and FIG. The Rth3 dependency of the viewing angle range obtained by adding up the polar angle observation angle ranges where x and y are 0.35 or less is shown. FIGS. 6a and 6b show the relationship between Rth1 and Rth3, Rth1 and Rth3 under the condition that there is less change in color tone at a polar angle observation angle deeper than that of the second comparative example when Rth1 of the negative biaxial film is added to the parameters. It is the graph put together as a relationship with Rth2. FIG. 7a shows the thickness direction retardation Rth3 dependence of the maximum value of polar angle observation angle with x and y chromaticity in the right direction being 0.35 or less, and FIG. The Rth3 dependency of the viewing angle range obtained by adding the maximum values of polar angle observation angles in which the x and y chromaticities are 0.35 or less is shown. FIG. 8a shows the relationship between the retardation Δnd of the liquid crystal layer and the total Rth, and FIG. 8b shows the relationship between the thickness direction retardation Rth3 of the second C plate and the total Rth. FIG. 8c shows the relationship between the retardation Δnd of the liquid crystal layer and the second C plate Rth3 by synthesizing the relationship shown in FIGS. 8a and 8b. 8d and 8e show the relationship between an appropriate in-plane retardation Re and thickness direction retardation Rth1. 9a and 9b are tables summarizing suitable conditions such as retardation in the thickness direction of the optical film.

  A liquid crystal display device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic perspective view showing a panel structure of a liquid crystal display device according to an embodiment. A vertical alignment (VA) mode liquid crystal cell 4 is disposed between the front-side polarizing plate 1 and the back-side polarizing plate 6 which are arranged in crossed Nicols.

  Between the front-side polarizing plate 1 and the liquid crystal cell 4, a first optical film 2 that is a negative biaxial film and a second optical film 3 that is a C plate are laminated and disposed. The 1st optical film 2 is arrange | positioned orthogonally to the polarizing plate absorption axis 1a which adjoins the front side polarizing plate 1, and the in-plane slow axis 2a adjoins. The in-plane slow axis 3a of the C plate 3 is preferably arranged in parallel or perpendicular to the slow axis 2a of the adjacent first optical film 2.

  A third optical film 5 that is a C plate is inserted between the liquid crystal cell 4 and the back-side polarizing plate 6. The in-plane slow axis 5 a of the third optical film 5 is arranged in parallel or orthogonal to the absorption axis 6 a of the adjacent back side polarizing plate 6.

  When a voltage equal to or higher than the threshold value of the liquid crystal material is applied between the electrodes disposed on the inner surfaces of the back and front substrates, the liquid crystal layer of the liquid crystal cell 4 is applied to the absorption axis 1 a of the front side polarizing plate 1 and the absorption axis 6 a of the back side polarizing plate 6. In contrast, the structure is inclined in the 45 ° direction.

  FIG. 1 illustrates a monodomain VA mode cell 4 in which an orientation process is performed on the back and front substrates to develop a pretilt angle. The orientation direction is indicated by arrows 4u and 4l. The VA mode liquid crystal cell 4 may have a multi-domain alignment structure in which alignment control elements such as openings or protrusions are regularly arranged on the front and back electrode surfaces.

  Front side polarizing plate 1, first optical film 2 that is negative biaxial film, second optical film 3 that is C plate, VA mode liquid crystal cell 4, third optical film 5 that is C plate, and backside polarized light The plate 6 forms the liquid crystal display element according to the embodiment.

  In the liquid crystal display device of FIG. 1, the orientation orientation of the back substrate is the lower orientation, the orientation orientation of the front substrate is the upper orientation, the orientation obtained by rotating the orientation orientation of the front substrate 90 ° clockwise is 90 ° clockwise and counterclockwise. Rotated direction is defined as left direction.

  The VA mode liquid crystal cell 4 is assumed to have a liquid crystal layer retardation Δnd of a high Δnd of 600 nm or more. The control device 7 multiplex-drives the VA mode liquid crystal cell 4. The duty of the multiplex drive is assumed to be a high duty with a duty ratio of 1/64 or more. In addition, it is called a high duty, so that the duty which is a denominator of a duty ratio is large.

  In the panel structure of this example, the expressions “parallel”, “orthogonal”, and “45 °” are used for the arrangement of each component. However, the angular arrangement in the actual production of the liquid crystal display element has a variation of about ± 2 to 3 °. Therefore, the angular relationship of 0 ° ± 3 ° is defined as “substantially parallel”, the angular relationship of 90 ° ± 3 ° is defined as “substantially orthogonal”, and the angular relationship of 45 ° ± 3 ° is defined as “substantially 45 °”.

  In the panel structure of this example, the expression “cross Nicol arrangement” is used for the back and front polarizing plates. However, when the liquid crystal display element is actually manufactured, the angular arrangement of the absorption axes has a variation of about 90 ° ± 3 °. Therefore, an arrangement in which the angle range formed by the absorption axes is 90 ° ± 3 ° (substantially orthogonal) is defined as “crossed Nicols arrangement”.

  The liquid crystal display element by an Example was produced in the following processes as an example. After forming a vertical alignment film made by Nissan Chemical on a glass substrate on which a transparent electrode having a desired pattern is formed, the column “Best Mode for Carrying Out the Invention” in JP-A-2005-234254 The substrate was subjected to orientation treatment by the rubbing treatment method shown in FIG. Note that an insulating film such as silicon oxide may be formed between the glass substrate and the alignment film.

  Thereafter, the two glass substrates were bonded to each other with a sealing material so that the vertical alignment film was close to the upper and lower surfaces and the rubbing direction was antiparallel. The space between the upper and lower glass substrates is controlled by a spherical spacer so as to be 4 μm to 6 μm.

  After injecting a liquid crystal material having a birefringence anisotropy Δn of 0.1 or more and 0.27 or less and a negative dielectric anisotropy Δε between two glass substrates, it is about 20 from the isotropic phase temperature of the liquid crystal material. Firing was carried out at a high temperature for 1 hour. The pretilt angle was 89.85 ° ± 0.1 ° in the liquid crystal cell plane regardless of the values of Δn and Δε of the liquid crystal material.

  A polarizing plate is bonded to the outside of the two glass substrates so that the polarizing plate absorption axis is in a substantially crossed Nicols arrangement. The polarizing plate used was VHC13U made by Polatechno. A TAC base film with Re of about 3 nm to 5 nm exists on the glass substrate bonding surface of the polarizing plate, and is bonded to the lower layer with an adhesive material. A negative biaxial film and a C plate were obtained by biaxially stretching a norbornene COP film. The light source of the backlight was a standard light source C.

  Next, liquid crystal display elements according to the first comparative example and the second comparative example will be described with reference to FIGS. 2 and 3 are schematic perspective views showing the panel structures of the liquid crystal display elements according to the first comparative example and the second comparative example, respectively.

  The liquid crystal display element of the 1st comparative example shown in FIG. 2 has the laminated structure which abbreviate | omitted the 2nd optical film 3 which is C plate from the liquid crystal display element of an Example.

  The liquid crystal display element of the 2nd comparative example shown in FIG. 3 has the laminated structure which abbreviate | omitted the 3rd optical film 5 which is C plate from the liquid crystal display element of an Example.

  In both the first comparative example and the second comparative example shown in FIGS. 2 and 3, the orientation relationship of the liquid crystal display elements is the same as that of the embodiment shown in FIG.

  A problem occurring in the liquid crystal display element of the comparative example will be described. In the structures of the first and second comparative examples, when the VA mode liquid crystal display device exhibiting high Δnd is multiplexed and driven at a high duty, the viewing angle characteristics of the display unit in the bright display state are observed. The color shift was observed as the polar angle became deeper with respect to the line, and it was found that the display quality deteriorated.

  When the arrangement structure of the optical film (viewing angle compensator) according to the first comparative example was adopted, a tendency was observed in which the transmittance was lowered due to color shift to yellow, green, blue, etc. as the observation angle was increased. Further, in the viewing angle compensator arrangement structure of the second comparative example, it was observed that the color shifted to yellow and the transmittance increased as the observation angle was deepened.

  As will be described below, according to the research of the present inventor, the viewing angle compensator arrangement structure according to the embodiment is used by appropriately setting the optical film characteristics such as thickness direction retardation, and thereby using a high Δnd (600 nm or more). ) VA mode liquid crystal display element when the multiplex driving is performed with a high duty (with a duty of 64 or more), it was found that the change in the viewing direction of the bright display portion, that is, the color shift with respect to the change in viewing angle, and the transmittance change can be suppressed. .

Next, based on simulation analysis, conditions for suppressing color shift and transmittance change with respect to viewing angle change will be considered. In this simulation analysis, the liquid crystal panel structure is the same as the actual liquid crystal display element described above. However, the glass substrate and the transparent electrode are omitted. The polarizing plate was Vola13 made by Polatechno, and the TAC base film had Re of 3 nm and Rth of 50 nm. The negative biaxial film and the C plate were obtained by biaxially stretching a norbornene-based COP film. The light source of the backlight was a standard light source C. Analysis was performed using a liquid crystal display simulator LCDMASTER8 manufactured by Shintech.
(1) In the case where Δnd is fixed to 1050 nm In the liquid crystal display element structure of the embodiment shown in FIG. 1, the retardation Δnd of the liquid crystal layer is set to 1050 nm, the in-plane retardation Re of the negative biaxial film 2 is 45 nm, and the thickness is The vertical phase difference Rth1 was fixed at 440 nm. When the thickness direction phase difference Rth2 of the first C plate 3 and the thickness direction phase difference Rth3 of the second C plate 5 change, the 180 ° azimuth (hereinafter referred to as the left azimuth) during bright display and 0 ° The viewing angle characteristics of the transmittance during bright display when the polar angle was changed with reference to the normal direction of the display surface of the liquid crystal display element in the azimuth direction (hereinafter referred to as the right azimuth) were calculated. Note that Rth1 = Rth2 + Rth3. That is, Rth1 + Rth2 + Rth3 = 880 nm.

  FIG. 4 a shows the left-right azimuth viewing angle characteristics when the transmittance during frontal observation is set to 7%. When the polar angle is negative, it represents the left direction, and when it is positive, the right direction. The case where the thickness direction retardation Rth3 of the second C plate is 0 nm corresponds to the second comparative example (FIG. 3). In the case of viewing angle compensation according to the second comparative example, the transmittance greatly increases when the observation angle is increased (deep) from about ± 25 ° polar angle, and the transmittance is more than double that of the frontal observation around ± 50 °. I understand that.

  As the value of Rth3 increases, the maximum transmittance when the observation angle becomes deeper decreases. The case where the thickness direction retardation Rth3 of the second C plate reaches 440 nm and the thickness direction retardation Rth2 = 0 nm of the first C plate corresponds to the first comparative example (FIG. 2). In the case of viewing angle compensation according to the first comparative example, a change is observed until there is an observation angle at which the transmittance is almost zero at a deep observation angle.

  With the setting of Rth2 and Rth3, a large change is observed in the transmittance at a deep observation angle, and at the same time, a large change appears in the color tone of the bright display state. It is also affected by the transmittance during frontal observation. Therefore, when the transmittance at the time of frontal observation is 3%, 5%, 7%, and 10%, the chromaticity x and y in the XYZ color system with respect to the change in the left and right azimuth polar angle observation angle when Rth2 and Rth3 are changed. And the left and right azimuth polar observation angles at which both x and y were within 0.35 were determined.

  4b and 4c show the thickness direction phase difference Rth3 of the second C plate having the maximum left and right azimuth polar angle observation angles where x and y are 0.35 or less when transmittance is used as a parameter. Indicates dependency. As described above, Rth3 = 0 nm corresponds to the viewing angle compensation method according to the second comparative example, and Rth3 = 440 nm corresponds to the viewing angle compensation method according to the first comparative example.

  Although a slight difference was observed depending on the transmittance, a close tendency was observed. When comparing the two comparative examples, the viewing angle compensation method of the second comparative example in which Rth3 = 0 nm has a color tone in a wider polar angle observation angle range than the viewing angle compensation method of the first comparative example in which Rth3 = 440 nm. There is a tendency for the change to be small.

  In the first comparative example, not only yellowing but also a color shift to various colors such as blue, red, and purple is observed, and the second comparative example tends to be smaller in color shift than the first comparative example. I found out. Therefore, the second comparative example is used as a reference, and the discussion is continued focusing on the condition that the color change can be further reduced as compared with the second comparative example.

  In the viewing angle compensation method of the embodiment in which Rth3 is between 0 nm and 440 nm, regarding the left azimuth, if the front transmittance is 5% or less, Rth3 is 147 nm (lower limit) to 293 nm (upper limit), 10% or less. When Rth3 is in the range of 147 nm (lower limit) to 220 nm (upper limit), the change in color tone is small in the wide polar angle observation angle range as compared with the second comparative example. When 147 nm (lower limit) to 293 nm (upper limit) and 10% or less, Rth3 is in the range of 147 nm (lower limit) to 220 nm (upper limit), and the change in color tone is small in a wide polar angle observation angle range as compared with the second comparative example. Note that in a region having a wider viewing angle range than the second comparative example, Rth3 when the viewing angle range is the smallest is expressed as a lower limit, and Rth3 having the widest viewing angle range is expressed as an upper limit.

  FIG. 4d shows the thickness direction phase difference Rth3 dependency of the second C plate when the sum of polar angle observation angle ranges where x and y are 0.35 or less in the left-right viewing angle characteristic is set as the viewing angle range. Show. In the viewing angle compensation method according to the second comparative example in which Rth3 = 0 nm, the polar angle observation angle range (viewing angle range) is in the range of 95 ° to 100 ° without largely depending on the transmittance during frontal observation. On the other hand, in the viewing angle compensation method according to the example, a wider viewing angle range than that of the first comparative example is obtained when Rth3 is in the range of 147 nm (lower limit) to 220 nm (upper limit). In particular, when Rth3 = 220 nm, it was possible to realize a viewing angle range of 120 ° or more.

  Reference is again made to FIG. As described with reference to FIGS. 4B to 4D, the viewing angle compensation method according to the second comparative example in which the thickness direction retardation Rth3 of the second C plate is 0 nm, and the thickness direction position of the first C plate According to the conditions of the embodiment with the viewing angle compensation method according to the first comparative example in which the phase difference Rth2 = 0 nm (thickness direction phase difference Rth3 = 440 nm of the second C plate), the color tone change in a wide polar angle observation angle range It turned out that it can suppress. In particular, when Rth3 = 220 nm, it was possible to realize a viewing angle range of 120 ° or more.

  Looking at the transmittance characteristics shown in FIG. 4a, it is shallow in the example between the second comparative example in which the transmittance greatly increases at a deep observation angle and the first comparative example in which the transmittance is greatly reduced at a deep observation angle. It can be seen that the transmittance characteristic as averaged from the observation angle to the deep observation angle is obtained. It can be seen that the transmittance characteristics are also averaged particularly well at Rth3 = 220 nm, which shows that the change in color tone can be suppressed particularly well in a wide polar angle observation angle range. Thus, it was found that the condition that can suppress the color tone change accompanying the viewing angle change can also suppress the transmittance change accompanying the viewing angle change.

  Next, the visual angle characteristics when the thickness direction retardation Rth2 and Rth3 of the first and second C plates were changed using the thickness direction retardation Rth1 of the negative biaxial film as a parameter were examined. The negative biaxial film had four Rth1 values of 300 nm, 220 nm, 120 nm, and 50 nm. At this time, the in-plane retardation Re was set to 50 nm, 55 nm, 80 nm, and 100 nm, respectively, at which good viewing angle characteristics can be realized at each Rth1. In this study, each parameter was changed so that Rth1 + Rth2 + Rth3 = 880 nm. The front transmittance was fixed at 7%.

  FIG. 5a shows the dependency of the maximum polar angle observation angle at which the chromaticity x, y in the left azimuth is 0.35 or less on the thickness direction retardation Rth3 of the second C plate. The case of Rth3 = 0 nm corresponds to the viewing angle compensation method according to the second comparative example. Some variation is caused by the thickness direction retardation Rth1 of the negative biaxial film, but its dependence is small.

  When Rth3 is 277 nm or more and 633 nm or less, x and y are 0.35 or less within the polar angle observation angle range narrower than that of the second comparative example, but other ranges, that is, Rth3 is 92 nm (lower limit) to 253 nm. (Upper limit) and 646 nm (lower limit) to 830 nm (upper limit), a tendency that no color change was observed up to a polar angle observation angle equal to or deeper than that of the second comparative example was observed. In particular, when Rth3 was in the range of 184 nm (lower limit) to 253 nm (upper limit) and 646 nm (lower limit) to 660 nm (upper limit), the polar angle observation angle was wider than that of the second comparative example under all Rth1 conditions.

  FIG. 5b shows the Rth3 dependency of the viewing angle range obtained by adding up the polar angle observation angle ranges in which x and y in the left and right viewing angle characteristics are 0.35 or less, similar to that shown in FIG. 4d. It was Rth3 in the range of 92 nm (lower limit) to 253 nm (upper limit) and 646 nm (lower limit) to 760 nm (upper limit) that can obtain a wider viewing angle range than the second comparative example regardless of the size of Rth1.

  When the negative biaxial film Rth1 is added to the parameters, the conditions of less color change at the polar angle observation angle deeper than those of the second comparative example are summarized as the relationship between Rth1 and Rth3 and the relationship between Rth1 and Rth2. The graphs are FIGS. 6a and 6b.

  FIG. 6a summarizes the relationship between Rth1 and Rth3. There are two types of Rth3 range (illustrated by surroundings) in which the color tone change is small at a deep polar angle, ie, a region where Rth3 is small and a region where Rth3 is large.

  In the region where Rth3 is small, both the upper limit and the lower limit are substantially constant ranges that do not depend on Rth1, and are generally included in the illustrated belt-like range of 73 nm (lower limit) ≦ Rth3 ≦ 253 nm (upper limit).

  On the other hand, in the range where Rth3 is large, the lower limit does not depend on Rth1 and is 633 nm, and the upper limit varies depending on the magnitude of Rth1, and can be expressed by a linear function of Rth3 = 880−Rth1. That is, a range of 633 nm (lower limit) ≦ Rth3 <880−Rth1 (upper limit) is preferable.

  FIG. 6b summarizes the relationship between Rth1 and Rth2. In the deep polar angle observation range, there are two regions (illustrated by surroundings), a band-like region extending from the upper left to the lower right, and a region where both Rth2 and Rth1 are small.

  The band-like region extending from the upper left to the lower right is included in the range of 668.03-1.009 Rth1 (lower limit) ≧ Rth2 ≧ 762.5-0.92079 Rth1 (upper limit) when linear function fitting is performed by the least square method.

On the other hand, the region where Rth1 and Rth2 are small is included in the range of 0 (lower limit) <Rth2 ≦ 247.09−1.1007 Rth1 (upper limit). At this time, Rth3 is included in the range of (Δnd−70) −Rth1−Rth2 ≦ Rth3 ≦ (Δnd−270) −Rth1−Rth2.
(2) When Δnd is changed In the above examination, Δnd was fixed at 1050 nm. Below, the result of having examined about the case where (DELTA) nd is changed into another value is shown.

  First, when retardation Δnd = 850 nm of the liquid crystal layer and Re / Rth1 of 55 nm / 220 nm and 45 nm / 440 nm are used for the negative biaxial film, the thickness direction retardations Rth2, Rth3 of the first and second C plates The viewing angle characteristics at that time were calculated. Rth1 + Rth2 + Rth3 = 660 nm. The transmittance during bright display during front observation was fixed at 7%.

  FIG. 7a shows the dependence of the maximum value of polar angle observation angle with right and left x, y chromaticity of 0.35 or less on the thickness direction retardation Rth3 of the second C plate. The time when Rth3 = 0 nm corresponds to the viewing angle compensation method according to the second comparative example. It was found that a tendency of the negative biaxial film independent of Rth1 was observed.

  FIG. 7b shows the Rth3 dependency of the viewing angle range obtained by adding up the maximum polar angle observation angles where the x and y chromaticities in the horizontal direction are 0.35 or less. In the second comparative example in which Rth3 = 0 nm, the viewing angle range was 115 °. However, the conditions of the example for realizing a wider viewing angle range were Rth3 of 73 nm (lower limit) to 147 nm (upper limit).

  Next, FIG. 8a shows the result of calculating the relationship between the retardation Δnd of the liquid crystal layer and the sum Rth of the thickness direction retardations Rth1, Rth2, and Rth3 in the negative biaxial film and the first and second C plates. . Here, Rth1 = 440 nm. In the graph, the optimum conditions and the upper and lower limits are shown. This is the optimum condition under which the background transmittance is the lowest when observing the left and right azimuth polar angles of 50 °, and Δnd is twice the transmittance. The lower limit and the upper limit are shown respectively.

  When the plot is fitted with a linear function, the total Rth can realize a favorable viewing angle characteristic within the range indicated by −319.23 + 1.374Δnd (lower limit) ≦ total Rth ≦ −111.76 + 1.0374Δnd (upper limit).

  The relationship between the thickness direction retardation Rth3 of the second C plate at this time and the combined Rth is as shown in FIG. 8b when the thickness direction Rth1 of the negative biaxial film is 220 nm and 440 nm. It is in. That is, it hardly depends on Rth1 of the negative biaxial film, and Rth3 has a color change within the range of 73 nm (lower limit) ≦ Rth3 ≦ 0.3336 (total Rth−70.4 (upper limit)) by linear function fitting. There is a range (illustrated with a box) that can be suppressed.

  FIG. 8c shows the relationship between the retardation Δnd of the liquid crystal layer and the second C plate Rth3 by synthesizing the relationships shown in FIGS. 8a and 8b.

  Rth3 suppresses color change in a polar angle observation angle range in which the region included in the range of 73 nm ≦ Rth3 ≦ −107.67 + 0.360909Δnd (illustrated by the box) is wider than that of the first comparative example by linear function fitting. it can. At this time, the range of Rth2 is (Δnd−70) −Rth1−Rth3 ≦ Rth2 ≦ (Δnd−270) −Rth1−Rth3.

  In the above study, the relationship between an appropriate in-plane retardation Re and thickness direction retardation Rth1 in a negative biaxial film was calculated and used. FIG. 8d shows the Rth1 dependency of Re appropriate for the liquid crystal display element structure of the example.

The appropriate Re by polynomial function curve fitting
Re ≧ 117.08−0.47257Rth1 + 0.0000094847Rth1 ^ 2−3.2179e−7Rth1 ^ 3
Re ≦ 127.08−0.47257Rth1 + 0.0000094847Rth1 ^ 2−6.2179e−7Rth1 ^ 3
It was the range enclosed by.

  In the above examination, the negative biaxial film uses a structure bonded to a polarizing plate having a TAC film as a base film, but the polarizing layer and the negative biaxial film are directly bonded except for the TAC film. Alternatively, a viewing angle compensation plate-integrated polarizing plate may be used. FIG. 8e shows the appropriate Rth1 dependency of Re in that case.

The appropriate Re by polynomial function curve fitting
Re ≧ 129.24−0.337045Rth1−0.0000033099Rth1 ^ 2 + 3.1872e-6Rth1 ^ 3-3.3891e-9Rth1 ^ 4
Re ≦ 139.24−0.337045Rth1−0.0000033099Rth1 ^ 2 + 3.1872e-6Rth1 ^ 3-3.3891e-9Rth1 ^ 4
It was the range enclosed by.

  In FIG. 6a, there is a condition that can suppress a change in color tone with respect to a change in viewing angle even under a condition where Rth3 is large. However, in this examination condition, Δnd is fixed at 1050 nm. When Δnd is included in the variable, the relationship between Rth1 and Rth3 is 633 nm ≦ Rth3 <(Δnd−170) −1.0921Rth1 when Δnd> 850 nm, and Rth2 at this time is (Δnd−70) −Rth1−Rth3 ≦ Rth2 ≦ (Δnd-270) −Rth1−Rth3 was within an appropriate range.

  As described above according to the simulation analysis results, in the arrangement structure of the viewing angle compensation plate according to the embodiment as shown in FIG. 1, the first optical film which is a negative biaxial film, the second which is a C plate. By appropriately selecting the thickness direction retardations Rth1, Rth2, Rth3, etc. of the third optical film which is a C plate, the color shift at the time of changing the viewing angle can be suppressed.

  Further, the change in transmittance at the time of changing the viewing angle can be suppressed under the condition that the color shift at the time of changing the viewing angle can be suppressed (as described with reference to FIGS. 4A to 4D).

  A liquid crystal display element with Rth1 = 440 nm (Re1 = 45 nm), Rth2 = Rth3 = 220 nm, and Δnd = 1050 nm was actually fabricated and the appearance was observed when the transmittance was set to 5%. It was confirmed that the color shift was suppressed.

  In addition, in the above examination, although the norbornene-type cyclic olefin resin biaxially-stretched was assumed as C plate, it is not the limitation. For example, it may be a stretched TAC film or an orientation-controlled cholesteric or discotic liquid crystal polymer.

  The table of FIG. 9a and FIG. 9b summarizes suitable conditions derived based on the above considerations and the like.

  8d and 8e, the lower limit of the appropriate in-plane retardation Re1 in the negative biaxial film is 40 nm. The upper limit is 120 nm, which shows the maximum Re1 in FIG. 8e. Therefore, an appropriate in-plane retardation Re1 of the negative biaxial film is 40 nm ≦ Re1 ≦ 120 nm.

  The thickness direction retardation Rth1 of the negative biaxial film is set, for example, between a lower limit of 50 nm in the simulation and an upper limit of 500 nm at which optical parameter uniformity is easily obtained. That is, 50 nm ≦ Rth1 ≦ 500 nm.

  The first viewing angle compensation technique (see FIG. 9a / Condition 1) includes a polarizing plate arranged on the back surface of a liquid crystal display element having a vertically aligned liquid crystal layer having a retardation of 600 nm or more and arranged in a crossed Nicol arrangement. A first optical film having an optical anisotropy of nx> ny ≧ nz and a second optical film having an optical anisotropy of nx≈ny> nz between the one polarizing plate and the liquid crystal cell are the first. The optical film is disposed so as to be close to the polarizing plate, the in-plane slow axis of the first optical film is substantially perpendicular to the adjacent polarizing plate absorption axis, and the other polarizing plate and the liquid crystal cell A third optical film having an optical anisotropy of nx≈ny> nz is disposed therebetween, the in-plane retardation Re1 of the first optical film is 40 nm ≦ Re1 ≦ 120 nm, and the thickness direction retardation Rth1 is 50 nm. ≦ R h1 ≦ 500 nm, the thickness direction retardation Rth3 of the third optical film is 73 nm ≦ Rth3 ≦ −107.67 + 0.360909nd, and the thickness direction retardation Rth2 of the second optical film is (Δnd−70) −Rth1−Rth3 ≦ Rth2 ≦ (Δnd−270) −Rth1−Rth3 provides a viewing angle compensation effect that suppresses a color shift and a transmittance change during a viewing angle change in bright display during multiplex driving with a duty of 1/64 duty or more. be able to.

  The second viewing angle compensation technique (see FIG. 9b / Condition 2) is that a polarizing plate is arranged on the back surface of a liquid crystal display element having a vertically aligned liquid crystal layer with a retardation of the liquid crystal layer larger than 850 nm and arranged in crossed Nicols. A first optical film having an optical anisotropy of nx> ny ≧ nz and a second optical film having an optical anisotropy of nx≈ny> nz between the one polarizing plate and the liquid crystal cell are the first. The optical film is disposed so as to be close to the polarizing plate, the in-plane slow axis of the first optical film is substantially perpendicular to the adjacent polarizing plate absorption axis, and the other polarizing plate and the liquid crystal cell A third optical film having an optical anisotropy of nx≈ny> nz is disposed therebetween, the in-plane retardation Re1 of the first optical film is 40 nm ≦ Re1 ≦ 120 nm, and the thickness direction retardation Rth1 is 50 nm. Rth1 ≦ 500 nm, the thickness direction retardation Rth3 of the third optical film is 633 nm ≦ Rth3 <(Δnd−170) −1.0921Rth1, and the thickness direction retardation Rth2 of the second optical film is (Δnd−70). ) −Rth1−Rth3 ≦ Rth2 ≦ (Δnd−270) −Rth1−Rth3, the viewing angle that suppresses the color shift and the transmittance change at the time of viewing angle change in bright display in multiplex driving of 1/64 duty or more. A compensation effect can be provided.

  The technique of the said Example can be utilized for the information display apparatus for vehicle-mounted information display apparatuses, industrial equipment, and household appliances, for example.

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

1 Front-side polarizing plate 2 First optical film (negative biaxial film)
3 Second optical film (first C plate)
4 VA mode liquid crystal cell 5 Third optical film (second C plate)
6 Back side polarizing plate 7 Control device

Claims (5)

A first polarizing plate and a second polarizing plate arranged in crossed Nicols,
A vertically aligned liquid crystal cell disposed between the first polarizing plate and the second polarizing plate;
It has optical anisotropy of nx> ny ≧ nz, and an in-plane slow axis is substantially orthogonal to the absorption axis of the first polarizing plate between the first polarizing plate and the vertically aligned liquid crystal cell. A first optical film arranged to
a second optical film having an optical anisotropy of nx≈ny> nz and disposed between the first optical film and the vertically aligned liquid crystal cell;
a third optical film having an optical anisotropy of nx≈ny> nz and disposed between the vertical alignment liquid crystal cell and the second polarizing plate;
The vertical alignment liquid crystal cell is
The retardation Δnd of the liquid crystal layer is 600 nm or more,
The first optical film is
In-plane retardation Re1 is 40 nm ≦ Re1 ≦ 120 nm,
Thickness direction retardation Rth1 is 50 nm ≦ Rth1 ≦ 500 nm,
The second optical film is
The thickness direction retardation Rth2 is (Δnd−70) −Rth1−Rth3 ≦ Rth2 ≦ (Δnd−270) −Rth1−Rth3,
The third optical film is
The thickness direction retardation Rth3 is 73 nm ≦ Rth3 ≦ −107.67 + 0.334609Δnd.
Liquid crystal display element. A first polarizing plate and a second polarizing plate arranged in crossed Nicols,
A vertically aligned liquid crystal cell disposed between the first polarizing plate and the second polarizing plate;
It has optical anisotropy of nx> ny ≧ nz, and an in-plane slow axis is substantially orthogonal to the absorption axis of the first polarizing plate between the first polarizing plate and the vertically aligned liquid crystal cell. A first optical film arranged to
a second optical film having an optical anisotropy of nx≈ny> nz and disposed between the first optical film and the vertically aligned liquid crystal cell;
a third optical film having an optical anisotropy of nx≈ny> nz and disposed between the vertical alignment liquid crystal cell and the second polarizing plate;
The vertical alignment liquid crystal cell is
The retardation Δnd of the liquid crystal layer is larger than 850 nm,
The first optical film is
In-plane retardation Re1 is 40 nm ≦ Re1 ≦ 120 nm,
Thickness direction retardation Rth1 is 50 nm ≦ Rth1 ≦ 500 nm,
The second optical film is
The thickness direction retardation Rth2 is (Δnd−70) −Rth1−Rth3 ≦ Rth2 ≦ (Δnd−270) −Rth1−Rth3,
The third optical film is
Thickness direction retardation Rth3 is 633 nm ≦ Rth3 <(Δnd−170) −1.0921Rth1.
Liquid crystal display element. In the first optical film, the in-plane retardation Re1 is relative to the thickness direction retardation Rth1,
Re1 ≧ 117.08−0.47257Rth1 + 0.0009847847Rth1 ^ 2-33.2179e-7Rth1 ^ 3
Re1 ≦ 127.08−0.47257Rth1 + 0.0000094847Rth1 ^ 2−6.2179e−7Rth1 ^ 3
The liquid crystal display element according to claim 1, wherein the relationship is satisfied. In the first optical film, the in-plane retardation Re1 is relative to the thickness direction retardation Rth1,
Re1 ≧ 129.24−0.337045Rth1−0.0000033099Rth1 ^ 2 + 3.1872e-6Rth1 ^ 3-3.3891e-9Rth1 ^ 4
Re1 ≦ 139.24−0.337045Rth1−0.0000033099Rth1 ^ 2 + 3.1872e-6Rth1 ^ 3-3.3891e-9Rth1 ^ 4
The liquid crystal display element according to claim 1, wherein the relationship is satisfied.   The material for the first to third optical films is a norbornene-based cyclic olefin resin, and is formed by stretching the films in two directions substantially orthogonal to each other. Liquid crystal display element.