Optical element and display device

Abstract

To provide an optical element that makes a light shielding region vertically asymmetric, while suppressing light leakage in an oblique direction vertically, and can further suppress coloring in the oblique direction, and a display device.SOLUTION: An optical element includes a first polarizer, a first retardation layer, a negative C plate, a second retardation layer, a second polarizer, a third retardation layer, a fourth retardation layer, and a third polarizer in this order. Tilt angles of first anisotropic molecules become larger from the first polarizer side toward the negative C plate side, and tilt angles of second anisotropic molecules become larger from the second polarizer side toward the negative C plate side. Tilt angles of third anisotropic molecules become smaller from the second polarizer side toward the fourth retardation layer side, and tilt angles of fourth anisotropic molecules become smaller from the third polarizer side toward the third retardation layer side. Absorption axes or reflection axes of the first, second, and third polarizers are parallel to each other, the absorption axis or the reflection axis of the first polarizer and a slow axis of the first retardation layer are orthogonal to each other, slow axes of the first and second retardation layers are parallel, and an angle formed by intersection of slow axes of the third and fourth retardation layers is 10° or greater and 20° or smaller.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The following disclosure relates to an optical element and a display device including the optical element. [Background technology]

[0002] Conventionally, various display devices such as liquid crystal display devices and organic electroluminescence (EL: Electro-Luminescence) display devices have been widely used as devices for displaying images (moving images and still images). Optical elements are sometimes used to improve the visibility of such display devices.

[0003] For example, Patent Document 1 discloses a transparent optical element comprising, from the viewing side, a polarizing plate and at least one obliquely oriented retardation film, in that order, in which (i) the absorption axis of the polarizing plate and the slow axis of the obliquely oriented retardation film are in the ranges of +15 degrees to +55 degrees and -15 degrees to -55 degrees, respectively, and (ii) the obliquely oriented retardation film has an in-plane retardation of 110 nm to 240 nm and an average tilt angle γ relative to the film plane of 22 degrees to 55 degrees. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 110216 Summary of the Invention [Problem to be solved by the invention]

[0005] Liquid crystal display devices are broadly classified into reflective and transmissive types depending on the method of light transmission to the liquid crystal layer. Transmissive liquid crystal display devices are equipped with a backlight having a light source, and display is achieved by light emitted from the backlight passing through the liquid crystal layer. The backlight may be provided with a prism sheet (lens sheet) on the observation side of the light source to focus light from the light source to the front.

[0006] In backlights equipped with a prism sheet, light components with large polar angles incident on the prism sheet from the light source are scattered by the prisms (convex and concave structures) of the prism sheet, and instead of being focused in the front, may exit the prism sheet at an even larger polar angle. Such light components that are not focused by the lens sheet and leak out at a large polar angle are called "side lobe light." Side lobe light is essentially a light component unnecessary for image display and is prone to becoming stray light within the LCD panel. This causes light leakage of oblique light (light with a large polar angle) during black display, which can be one of the factors reducing contrast when viewed from an oblique direction.

[0007] According to the inventors' investigations, since side lobe light is likely to be generated in the vertical direction depending on the backlight configuration, there is room for further investigation to suppress light leakage in the diagonal direction in the vertical direction. Furthermore, in a usage mode in which a user observes an optical element from above or below, it is sometimes desirable to make the visibility when viewed from above asymmetric with the visibility when viewed from below. For example, when an optical element is used by being overlaid on an in-vehicle display, since the user observes the optical element from above, it is desirable that the visibility when viewed from above is higher than the visibility when viewed from below. Furthermore, according to the inventors' investigations, when viewed from an oblique direction, the displayed image may be colored in an unintended color, which leaves room for further investigation.

[0008] In the above-mentioned Patent Document 1, it is considered that a specific optical element is placed on the observation surface side of the display device to suppress a decrease in visibility due to reflection of external light, but it does not consider a decrease in contrast due to side lobe light, asymmetry in visibility in the up and down directions, or coloring in oblique directions.

[0009] The present invention has been made in consideration of the above-mentioned current situation, and aims to provide an optical element that can suppress light leakage in diagonal directions in the up and down directions while making the light-shielding area asymmetrical in the up and down directions and further suppressing coloring in diagonal directions, and a display device equipped with the optical element. [Means for solving the problem]

[0010] (1) One embodiment of the present invention includes a first polarizer, a first retardation layer including first anisotropic molecules, a negative C plate, a second retardation layer including second anisotropic molecules, a second polarizer, a third retardation layer including third anisotropic molecules, a fourth retardation layer including fourth anisotropic molecules, and a third polarizer, in this order, wherein the first anisotropic molecules change so that their tilt angles increase from the first polarizer side of the first retardation layer toward the negative C plate side, the second anisotropic molecules change so that their tilt angles increase from the second polarizer side of the second retardation layer toward the negative C plate side, and the third anisotropic molecules change so that their tilt angles decrease from the second polarizer side of the third retardation layer toward the fourth retardation layer side, and the fourth anisotropic molecules change so that their tilt angles decrease from the second polarizer side of the third retardation layer toward the fourth retardation layer side. the anisotropic molecules change so that the tilt angle decreases from the third polarizer side of the fourth retardation layer toward the third retardation layer side; the absorption axis or reflection axis of the first polarizer, the absorption axis or reflection axis of the second polarizer, and the absorption axis or reflection axis of the third polarizer are parallel to one another in a planar view; the absorption axis or reflection axis of the first polarizer is perpendicular to the slow axis of the first retardation layer in a planar view; the slow axis of the first retardation layer and the slow axis of the second retardation layer are parallel to one another in a planar view; the slow axis of the third retardation layer and the slow axis of the fourth retardation layer intersect in a planar view; and the angle formed by the slow axis of the third retardation layer and the slow axis of the fourth retardation layer is 10° or more and 20° or less.

[0011] (2) One embodiment of the present invention is an optical element having the configuration of (1) above, wherein an angle formed between a slow axis of the second retardation layer and a slow axis of the third retardation layer is 5° or more and 10° or less, and an angle formed between a slow axis of the first retardation layer and a slow axis of the fourth retardation layer is 5° or more and 10° or less.

[0012] (3) In one embodiment of the present invention, in addition to the configuration of (1) or (2), a surface of the first retardation layer on the first polarizer side is a first surface, a surface of the second retardation layer on the second polarizer side is a second surface, a surface of the third retardation layer on the second polarizer side is a third surface, a surface of the fourth retardation layer on the third polarizer side is a fourth surface, a direction along the major axis of the first anisotropic molecules projected onto the first surface from a side closer to the second surface of the first retardation layer to a side closer to the first surface is an orientation direction of the first anisotropic molecules, and a direction along the major axis of the second anisotropic molecules projected onto the first surface from a side closer to the second surface of the second retardation layer to a side closer to the first surface is an orientation direction of the first anisotropic molecules. When the orientation direction of the second anisotropic molecule is defined as the direction along the long axis of the third anisotropic molecule projected onto the second surface from the side closer to the fourth surface of the third retardation layer to the side closer to the third surface, the orientation direction of the third anisotropic molecule is defined as the direction along the long axis of the third anisotropic molecule projected onto the third surface from the side closer to the fourth surface of the third retardation layer to the side closer to the third surface, and the orientation direction of the fourth anisotropic molecule is defined as the direction along the long axis of the fourth anisotropic molecule projected onto the fourth surface from the side closer to the fourth surface of the fourth retardation layer to the side closer to the third surface, the orientation direction of the fourth anisotropic molecule is defined as the orientation direction of the fourth anisotropic molecule, the orientation direction of the first anisotropic molecule and the orientation direction of the second anisotropic molecule differ by 180°±3° in planar view.

[0013] (4) One embodiment of the present invention is an optical element having the configuration of (3) above, in which, when the horizontal right direction of the optical element as seen from the first polarizer side is defined as an azimuth angle of 0°, and when a counterclockwise angle from the azimuth angle of 0° is defined as a positive angle and a clockwise angle is defined as a negative angle, the orientation orientation of the first anisotropic molecule is 0°±3° and the orientation orientation of the second anisotropic molecule is 180°±3°, or the orientation orientation of the first anisotropic molecule is 180°±3° and the orientation orientation of the second anisotropic molecule is 0°±3°.

[0014] (5) One embodiment of the present invention is an optical element in which, in addition to the configuration of (3) or (4) above, when viewed in a plane, the third anisotropic molecule is oriented in a direction rotated by a predetermined angle in either a clockwise or counterclockwise direction relative to the orientation direction of the second anisotropic molecule, and when viewed in a plane, the fourth anisotropic molecule is oriented in a direction rotated by the predetermined angle in the other of the clockwise and counterclockwise directions relative to the orientation direction of the first anisotropic molecule.

[0015] (6) One embodiment of the present invention is an optical element having the configuration of (5) above, wherein the predetermined angle is equal to or greater than 5° and equal to or less than 10°.

[0016] (7) One embodiment of the present invention is an optical element having the configuration of any one of (1) to (6) above, wherein the thickness direction retardation of the negative C plate is 250 nm or more and 320 nm or less.

[0017] (8) One embodiment of the present invention is an optical element having any one of the configurations (1) to (7) above, wherein a rate of change in tilt angle of the first anisotropic molecules along the thickness direction of the first retardation layer from the first polarizer side to the negative C plate side is the same as a rate of change in tilt angle of the second anisotropic molecules along the thickness direction of the second retardation layer from the second polarizer side to the negative C plate side.

[0018] (9) One embodiment of the present invention is an optical element having any one of the configurations (1) to (8) above, wherein a rate of change in the tilt angle of the third anisotropic molecule from the fourth retardation layer side to the second polarizer side along the thickness direction of the third retardation layer is the same as a rate of change in the tilt angle of the fourth anisotropic molecule from the third retardation layer side to the third polarizer side along the thickness direction of the fourth retardation layer.

[0019] (10) One embodiment of the present invention is an optical element having the configuration of any one of (1) to (9) above, wherein the first polarizer is an absorptive polarizer, a reflective polarizer, or a laminate of an absorptive polarizer and a reflective polarizer; the second polarizer is an absorptive polarizer or a reflective polarizer; and the third polarizer is an absorptive polarizer, a reflective polarizer, or a laminate of an absorptive polarizer and a reflective polarizer.

[0020] (11) Another embodiment of the present invention is a display device comprising, in this order, a liquid crystal panel according to any one of (1) to (10) above, an optical element, and a backlight, the optical element being positioned so that the first polarizer faces the liquid crystal panel.

[0021] (12) One embodiment of the present invention is a display device in which, in addition to the configuration described in (11) above, the backlight includes an irradiation unit and a prism sheet arranged on the observation side of the irradiation unit, the prism sheet has multiple rows of linear convex portions extending parallel to each other on the surface on the observation side, and in a planar view, the absorption axis of the first polarizer is parallel to or perpendicular to the ridge line of the linear convex portions. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide an optical element that can suppress light leakage in diagonal directions in the vertical direction, while making the light-shielding area asymmetric in the vertical direction, and further suppressing coloring in diagonal directions, and a display device equipped with the optical element. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 2 is a diagram illustrating a polar angle and an azimuthal angle. [Figure 2] 1 is a cross-sectional view schematically illustrating an optical element according to a first embodiment. [Figure 3] FIG. 2 is an exploded plan view illustrating the slow axis of each retardation layer and the orientation direction of anisotropic molecules. [Figure 4] 3 is a diagram showing the axial orientations of the components of the optical element according to the first embodiment. FIG. [Figure 5]FIG. 10 is a cross-sectional view illustrating a display device according to a second embodiment. [Figure 6] FIG. 2 is a perspective view showing an example of a prism sheet provided in the backlight. [Figure 7] 10 is a diagram showing the axial orientations of the components of the optical element according to Comparative Example 1. FIG. [Figure 8] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 1. [Figure 9] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 2. [Figure 10] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 3. [Figure 11] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 4. [Figure 12] 10 shows the results of simulation of the transmittance, viewing angle, and coloring of the optical element of Comparative Example 5. [Figure 13] 1 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Example 1. [Figure 14] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Example 2. [Figure 15] 10 shows the results of simulation of the transmittance, viewing angle, and coloring of the optical element of Comparative Example 6. [Figure 16] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 7. [Figure 17] 10 is a graph showing the transmittance of the optical element of Comparative Example 1. [Figure 18] 4 is a graph showing the transmittance of the optical element of Example 1. [Figure 19] 10 is a graph showing the transmittance of the optical element of Example 2. [Figure 20] 10 shows the results of a simulation of the transmittance and viewing angle of the optical element of Comparative Example 8. [Figure 21] 1 is a graph showing the relationship between the rotation angle of the orientation direction of anisotropic molecules and the maximum transmittance relative ratio. [Figure 22]1 is a graph showing the relationship between the rotation angle of the orientation direction of anisotropic molecules and the transmittance at a polar angle of 60° at an azimuth angle of 90°. [Figure 23] 1 is a graph showing the relationship between the rotation angle of the orientation direction of anisotropic molecules and Δxy. [Figure 24] 10 is a graph showing the relationship between the retardation and transmittance in the thickness direction of a negative C plate. [Figure 25] 10 is a graph showing the relationship between the retardation in the thickness direction of a negative C plate and Δxy. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the contents described in the following embodiments, and appropriate design changes can be made within the scope of the configuration of the present invention. In the following description, the same reference numerals will be used in different drawings as appropriate for parts having the same or similar functions, and repeated explanations will be omitted as appropriate. Each aspect of the present invention may be combined as appropriate within the scope of the gist of the present invention.

[0025] [Term definition] FIG. 1 is a diagram illustrating polar angles and azimuth angles. In this specification, polar angle θ refers to the angle between a target direction (e.g., measurement direction F) and a direction parallel to the normal to the principal surface of an optical element, as shown in FIG. 1. That is, a direction parallel to the normal (z) to the principal surface (xy plane) of an optical element has a polar angle of 0°. A direction parallel to the normal is also called a normal direction. Furthermore, azimuth refers to the direction when the target direction is projected onto the principal surface of an optical element, and is expressed as an angle (also called an azimuth angle) between the target direction and a reference azimuth (azimuth angle 0°). The reference azimuth is set, for example, to the horizontal right direction when the optical element is viewed from the observer side.

[0026] In this specification, "two axes (directions) are parallel" means that the angle (absolute value) they form is within a range of 0±3°, preferably within a range of 0±1°, more preferably within a range of 0±0.5°, and particularly preferably 0° (completely parallel). In addition, "two axes (directions) are perpendicular to each other" means that the angle (absolute value) they form is within a range of 90±3°, preferably within a range of 90±1°, more preferably within a range of 90±0.5°, and particularly preferably 90° (completely perpendicular). Examples of the above axes include the transmission axis and reflection axis of a polarizer and the slow axis of a retardation layer.

[0027] In this specification, the birefringent layer refers to a layer in which either the in-plane retardation (in-plane retardation) Re or the absolute value of the thickness retardation Rth is 10 nm or more, preferably 20 nm or more. The birefringent layer includes a retardation layer and a negative C plate. The in-plane retardation Re, the thickness retardation Rth, and the NZ coefficient (biaxial parameter) of the birefringent layer are defined by the following formula, where d is the thickness of the birefringent layer, nx is the refractive index in the x-axis direction, ny is the refractive index in the y-axis direction, and nz is the refractive index in the z-axis direction. Note that ns refers to the larger of nx and ny, and nf refers to the smaller of nx and ny. Here, the x-axis is set at an azimuth angle of 0°-180°, the y-axis is set at an azimuth angle of 90°-270°, and the z-axis is perpendicular to the x-axis and y-axis. In this specification, unless otherwise specified, Re, Rth, and NZ coefficient are measured at 550 nm and at a temperature of 23° C. Unless otherwise specified, retardation refers to the in-plane retardation Re. Re=(ns-nf)×d Rth={nz-(nx+ny) / 2}×d NZ=(ns-nz) / (ns-nf)

[0028] "Azimuth angle A°-B°" refers to the direction along azimuth angle A° and azimuth angle B° in a planar view. In this specification, azimuth angles 0°-180° are also referred to as left-right azimuths, and azimuth angles 90°-270° are also referred to as up-down azimuths. An azimuth angle of 90° is also referred to as the upward direction, and an azimuth angle of 270° is also referred to as the downward direction.

[0029] In this specification, the observation surface side means the side of the target component that is closer to the observer when the target component is placed facing the observer, and the back side means the side of the target component that is farther from the observer.

[0030] (Embodiment 1) FIG. 2 is a cross-sectional schematic diagram of an optical element according to embodiment 1. As shown in FIG. 2, the optical element 100 according to embodiment 1 includes a first polarizer 10, a first retardation layer 20, a negative C plate 80, a second retardation layer 30, a second polarizer 40, a third retardation layer 50, a fourth retardation layer 60, and a third polarizer 70, in this order. Since the optical element 100 functions as an optical louver, a configuration including the components from the first polarizer 10 to the third polarizer 70 is also referred to as a polarizing plate louver. Furthermore, if a configuration including the first polarizer 10, the first retardation layer 20, the negative C plate 80, the second retardation layer 30, and the second polarizer 40, in this order, is considered to be one polarizing plate louver, and a configuration including the second polarizer 40, the third retardation layer 50, the fourth retardation layer 60, and the third polarizer 70, in this order, is considered to be another polarizing plate louver, the optical element 100 can also be considered to be an optical element in which two polarizing plate louvers are stacked. In the embodiment, the first polarizer 10 side of the optical element 100 is also referred to as the observation side, and the third polarizer 70 side is also referred to as the back side. The optical element 100 may be used so that the first polarizer 10 side is the back side and the third polarizer 70 side is the observation side. From the viewpoint of suppressing blue color when viewed from an oblique direction, it is preferable that the first polarizer 10 side is the observation side.

[0031] (polarizer) The first polarizer 10, the second polarizer 40, and the third polarizer 70 have the function of extracting polarized light (linearly polarized light) that vibrates only in a specific direction from unpolarized light (natural light), partially polarized light, or polarized light, and are also called linear polarizers. The first polarizer 10, the second polarizer 40, and the third polarizer 70 may each be an absorptive polarizer or a reflective polarizer. The absorptive polarizer has an absorption axis that absorbs light that vibrates in a specific direction and a transmission axis that transmits polarized light (linearly polarized light) that vibrates in a direction perpendicular to the specific direction. The reflective polarizer has a reflection axis that reflects light that vibrates in a specific direction and a transmission axis that transmits polarized light (linearly polarized light) that vibrates in a direction perpendicular to the specific direction.

[0032] The first polarizer 10, the second polarizer 40, and the third polarizer 70 may all be absorptive polarizers. By adopting such an embodiment, when a backlight is disposed on the rear side of the optical element 100, side lobe light can be absorbed, and the light blocking properties in oblique directions in the vertical direction can be further improved.

[0033] The first polarizer 10 may be an absorptive polarizer, and the third polarizer 70 may be a reflective polarizer. By using a reflective polarizer for the rear-side third polarizer 70, when a backlight is disposed on the rear side of the optical element 100, the side lobe light is reflected toward the backlight, and the reflected light is emitted again toward the observation surface by a reflector or the like of the backlight, thereby recycling the light and increasing the brightness in the normal direction during white display.

[0034] The first polarizer 10 may be an absorptive polarizer, a reflective polarizer, or a laminate of an absorptive polarizer and a reflective polarizer. The second polarizer 40 may be an absorptive polarizer or a reflective polarizer. The third polarizer 70 may be an absorptive polarizer, a reflective polarizer, or a laminate of an absorptive polarizer and a reflective polarizer. The polarizer arranged on the observation side is preferably an absorptive polarizer or a laminate of an absorptive polarizer and a reflective polarizer, and the polarizer arranged on the back side is preferably a reflective polarizer or a laminate of an absorptive polarizer and a reflective polarizer. When the first polarizer 10 is a laminate of an absorptive polarizer and a reflective polarizer, the absorptive polarizer and the reflective polarizer are preferably laminated in this order from the observation side. When the third polarizer 70 is a laminate of an absorptive polarizer and a reflective polarizer, the absorptive polarizer and the reflective polarizer are preferably laminated in this order from the observation side. Although reflective polarizers have the effect of improving the brightness in the normal direction during white display, they have a lower degree of polarization than absorptive polarizers, and therefore using only a reflective polarizer may result in a decrease in the contrast of the polarizing plate louver. Therefore, by laminating an absorptive polarizer and a reflective polarizer, it is possible to increase the brightness in the normal direction while also increasing the contrast. When an absorptive polarizer and a reflective polarizer are laminated, the transmission axis of the absorptive polarizer and the transmission axis of the reflective polarizer are parallel to each other.

[0035] It is more preferable that both the first polarizer 10 and the third polarizer 70 are laminates of an absorptive polarizer and a reflective polarizer. It is even more preferable that both the first polarizer 10 and the third polarizer 70 have a reflective polarizer laminated on the back side of the absorptive polarizer. In a display device in which a liquid crystal panel is disposed on the front side of an optical element and a backlight is disposed on the back side of the optical element, brightness and contrast can be further improved. By using a laminate of an absorptive polarizer and a reflective polarizer for the third polarizer 70 located on the backlight side, light emitted from the backlight can be more efficiently reflected toward the backlight, thereby improving light recycling efficiency. By using a laminate of an absorptive polarizer and a reflective polarizer for the first polarizer 10 located on the liquid crystal panel side, light incident from the backlight side can be further reflected toward the backlight, thereby improving the front brightness of the liquid crystal panel.

[0036] An example of an absorptive polarizer is one having a polarizing layer in which an anisotropic material such as a dichroic iodine complex is adsorbed and aligned on a polyvinyl alcohol (PVA) film. The polarizing layer may have a protective film such as a triacetyl cellulose (TAC) film on at least one of the viewing side and the back side.

[0037] Examples of reflective polarizers include reflective polarizers obtained by uniaxially stretching a co-extruded film made of multiple types of resins (e.g., APCF manufactured by Nitto Denko Corporation, DBEF manufactured by 3M, etc.), and reflective polarizers in which thin metal wires are periodically arranged (so-called wire grid polarizers).

[0038] (phase contrast layer) The first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60 have the function of changing the state of incident polarized light by applying a phase difference between two orthogonal polarized light components using a birefringent material or the like.

[0039] As shown in FIG. 2 , the first retardation layer 20 contains first anisotropic molecules 21, the second retardation layer 30 contains second anisotropic molecules 31, the third retardation layer 50 contains third anisotropic molecules 51, and the fourth retardation layer 60 contains fourth anisotropic molecules 61. The first anisotropic molecules 21 change so that their tilt angles increase from the first polarizer 10 side of the first retardation layer 20 toward the negative C plate 80 side of the first retardation layer 20. The second anisotropic molecules 31 change so that their tilt angles increase from the second polarizer 40 side of the second retardation layer 30 toward the negative C plate 80 side of the second retardation layer 30. The third anisotropic molecules 51 change so that their tilt angles decrease from the second polarizer 40 side of the third retardation layer 50 toward the fourth retardation layer 60 side of the third retardation layer 50. The fourth anisotropic molecules 61 change so that the tilt angle becomes smaller from the third polarizer 70 side of the fourth retardation layer 60 toward the third retardation layer 50 side of the fourth retardation layer 60. In this specification, planar view means that an object is viewed from the observation surface side.

[0040] In this specification, among the first anisotropic molecules 21 contained in the first retardation layer 20, the first anisotropic molecules located on the first polarizer 10 side of the first retardation layer 20 are referred to as first anisotropic molecules 21A, the first anisotropic molecules located on the negative C plate 80 side of the first retardation layer 20 are referred to as first anisotropic molecules 21B, and the tilt angle of the first anisotropic molecules 21A is referred to as θ 1-1 The tilt angle of the first anisotropic molecule 21B is θ 1-2 Of the second anisotropic molecules 31 contained in the dual retardation layer 30, the second anisotropic molecules located on the second polarizer 40 side of the second retardation layer 30 are referred to as second anisotropic molecules 31A, and the second anisotropic molecules located on the negative C plate 80 side of the second retardation layer 30 are referred to as second anisotropic molecules 31B. The tilt angle of the second anisotropic molecules 31A is referred to as θ 2-1 The tilt angle of the second anisotropic molecule 31B is θ 2-2 Of the third anisotropic molecules 51 contained in the third retardation layer 50, the third anisotropic molecules located on the second polarizer 40 side of the third retardation layer 50 are referred to as third anisotropic molecules 51A, and the third anisotropic molecules located on the fourth retardation layer 60 side of the third retardation layer 50 are referred to as third anisotropic molecules 51B. The tilt angle of the third anisotropic molecules 51A is referred to as θ 3-1 The tilt angle of the third anisotropic molecule 51B is θ 3-2 Of the fourth anisotropic molecules 61 contained in the fourth retardation layer 60, the fourth anisotropic molecule located on the third polarizer 70 side of the fourth retardation layer 60 is referred to as a fourth anisotropic molecule 61A, the fourth anisotropic molecule located on the third retardation layer 50 side of the fourth retardation layer 60 is referred to as a fourth anisotropic molecule 61B, and the tilt angle of the fourth anisotropic molecule 61A is referred to as θ 4-1 The tilt angle of the fourth anisotropic molecule 61B is θ 4-2 Let's say.

[0041] Unless otherwise specified, the tilt angle of the first anisotropic molecule 21 refers to the angle at which the long axis of the first anisotropic molecule 21 is inclined with respect to a plane parallel to the surface (first surface I) of the first retardation layer 20 facing the first polarizer 10. The tilt angle of the second anisotropic molecule 31 refers to the angle at which the long axis of the second anisotropic molecule 31 is inclined with respect to a plane parallel to the surface (second surface II) of the second retardation layer 30 facing the second polarizer 40. The tilt angle of the third anisotropic molecule 51 refers to the angle at which the long axis of the third anisotropic molecule 51 is inclined with respect to a plane parallel to the surface (third surface III) of the third retardation layer 50 facing the second polarizer 40. The tilt angle of the fourth anisotropic molecule 61 refers to the angle at which the long axis of the fourth anisotropic molecule 61 is inclined with respect to a plane parallel to the surface (fourth surface IV) of the fourth retardation layer 60 facing the third polarizer 70. The tilt angle is defined as 0° or more and 90° or less.

[0042] The first anisotropic molecules 21, the second anisotropic molecules 31, the third anisotropic molecules 51, and the fourth anisotropic molecules 61 are preferably oriented so that the tilt angles change continuously in the thickness directions of the first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60. A continuously changing tilt angle means that the anisotropic molecules are oriented so that the tilt angles gradually increase or decrease from one surface side to the other surface side of each retardation layer.

[0043] As shown in Figure 2, the above θ 1-1 is the above θ 1-2 smaller than the above θ 2-1 is the above θ 2-2 The above θ 3-1 is the above θ 3-2 The above θ4-1 is larger than the above θ 4-2 It can be said that the first anisotropic molecules 21, the second anisotropic molecules 31, the third anisotropic molecules 51, and the fourth anisotropic molecules 61 are hybrid-oriented in that the tilt angles are different in the thickness direction of the first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60, respectively. By hybrid-orienting the anisotropic molecules in each retardation layer and using an axial arrangement described below, it is possible to make the color of the optical element 100 when viewed from an oblique direction nearly monochrome.

[0044] The first retardation layer 20 and the negative C plate 80 may be in contact with each other, the negative C plate 80 and the second retardation layer 30 may be in contact with each other, and the third retardation layer 50 and the fourth retardation layer 60 may be in contact with each other.

[0045] It is preferable that the change in tilt angle of the first anisotropic molecules 21 and the second anisotropic molecules 31 is symmetrical in cross section. The rate of change in the tilt angle of the first anisotropic molecules 21, which changes from the first polarizer 10 side to the negative C plate 80 side along the thickness direction of the first retardation layer 20, is the same as the rate of change in the tilt angle of the second anisotropic molecules 31, which changes from the second polarizer 40 side to the negative C plate 80 side along the thickness direction of the second retardation layer 30. The rate of change in the tilt angle of the first anisotropic molecules can be expressed by the following formula (1), and the rate of change in the tilt angle of the second anisotropic molecules can be expressed by the following formula (2). The rate of change of the tilt angle of the first anisotropic molecule = θ 1-2 -θ 1-1 / Thickness of first retardation layer (μm) (1) The rate of change of the tilt angle of the second anisotropic molecule = θ 2-2 -θ 2-1 / Thickness of second retardation layer (μm) (2)

[0046] The third anisotropic molecule 51 and the fourth anisotropic molecule 61 preferably have symmetrical changes in tilt angle in cross section. The rate of change in the tilt angle of the third anisotropic molecule 51 along the thickness direction of the third retardation layer 50 from the fourth retardation layer 60 side to the second polarizer 40 side is preferably the same as the rate of change in the tilt angle of the fourth anisotropic molecule 61 along the thickness direction of the fourth retardation layer 60 from the third retardation layer 50 side to the third polarizer 70 side. The rate of change in the tilt angle of the third anisotropic molecule can be expressed by the following formula (3), and the rate of change in the tilt angle of the fourth anisotropic molecule can be expressed by the following formula (4). The rate of change of the tilt angle of the third anisotropic molecule = θ 3-1 -θ 3-2 / Thickness of the third retardation layer (μm) (3) The rate of change of tilt angle of the quaternary anisotropic molecule = θ 4-1 -θ 4-2 / Thickness of the fourth retardation layer (μm) (4)

[0047] The difference in thickness between the first retardation layer and the second retardation layer is preferably 1 μm or less, and more preferably both retardation layers have the same thickness.The difference in thickness between the third retardation layer and the fourth retardation layer is preferably 1 μm or less, and more preferably both retardation layers have the same thickness.

[0048] The direction of change in the tilt angle of the first anisotropic molecules 21 in the first retardation layer 20 is preferably the same as the direction of change in the tilt angle of the second anisotropic molecules 31 in the second retardation layer 30. Furthermore, the direction of change in the tilt angle of the third anisotropic molecules 51 in the third retardation layer 50 is preferably the same as the direction of change in the tilt angle of the fourth anisotropic molecules 61 in the fourth retardation layer 60.

[0049] The change direction of the tilt angle of the anisotropic molecules refers to the direction along the long axis of the anisotropic molecules projected onto one surface of the retardation layer from the side closer to the other surface to the side closer to the other surface. Here, the tilt angle of the anisotropic molecules on the one surface side is smaller than the tilt angle of the anisotropic molecules on the other surface side. In other words, the one surface can be said to be the surface on the side where the tilt angle of the anisotropic molecules is smaller, and the other surface can be said to be the surface on the side where the tilt angle of the anisotropic molecules is larger. In cross-sectional views (such as FIG. 2), the direction of the change in the tilt angle of the anisotropic molecules is indicated by the direction of the white arrow. The one surface refers to the surface of the first retardation layer 20 facing the first polarizer 10 (first surface I), the surface of the second retardation layer 30 facing the negative C plate 80 (second surface II), the surface of the third retardation layer 50 facing the fourth retardation layer 60, or the surface of the fourth retardation layer 60 facing the third retardation layer 50.

[0050] From the viewpoint of reducing the transmittance in the oblique direction in the up and down directions, the above θ 1-2 and the above θ 2-2 is preferably 65° or more and 90° or less. 1-2 and the above θ 2-2 is more preferably 70° or more and 80° or less.

[0051] The above θ 1-1 and the above θ 2-1 is the above θ 1-2 and the above θ 2-2 However, for example, the angle is preferably 0° or more and 10° or less, and more preferably 1° or more and 5° or less.

[0052] The above θ 1-1 and the above θ 2-1 The difference between the above θ is preferably 3° or less, more preferably 1° or less, 1-1 and the above θ 2-1 It is more preferable that the above θ 1-2 and the above θ 2-2 The difference between the above θ is preferably 3° or less, more preferably 1° or less, 1-2 and the above θ 2-2 It is more preferable that the above formulas are the same as those of the formulas.

[0053] From the viewpoint of reducing the transmittance in the oblique direction in the up and down directions, the above θ 3-1 and the above θ 4-1 is preferably 65° or more and 90° or less. 3-1 and the above θ 4-1 is more preferably 70° or more and 80° or less.

[0054] The above θ 3-2 and the above θ 4-2 is the above θ 3-1 and the above θ 4-1 However, for example, the angle is preferably 0° or more and 10° or less, and more preferably 1° or more and 5° or less.

[0055] The above θ 3-1 and the above θ 4-1 The difference between the above θ is preferably 3° or less, more preferably 1° or less, 3-1 and the above θ 4-1 It is more preferable that the above θ 3-2 and the above θ 4-2 The difference between the above θ is preferably 3° or less, more preferably 1° or less, 3-2 and the above θ 4-2It is more preferable that the above formulas are the same as those of the formulas.

[0056] The orientation direction of the anisotropic molecules will be described below. As shown in FIG. 2, the surface of the first retardation layer 20 on the first polarizer 10 side is referred to as the first surface I, the surface of the second retardation layer 30 on the second polarizer 40 side is referred to as the second surface II, the surface of the third retardation layer 50 on the second polarizer 40 side is referred to as the third surface III, and the surface of the fourth retardation layer 60 on the third polarizer 70 side is referred to as the fourth surface IV. The orientation direction of the first anisotropic molecules refers to the direction along the major axis of the first anisotropic molecules from the side closer to the second surface II of the first retardation layer toward the side closer to the first surface I, projected onto the first surface I. The orientation direction of the second anisotropic molecules refers to the direction along the major axis of the second anisotropic molecules from the side closer to the second surface II of the second retardation layer toward the side closer to the first surface I, projected onto the second surface II. The orientation direction of the third anisotropic molecules refers to the direction along the optical axis of the third anisotropic molecules of the third retardation layer, from the side closer to the fourth surface IV to the side closer to the third surface III, projected onto the third surface III. The orientation direction of the fourth anisotropic molecules refers to the direction along the optical axis of the fourth anisotropic molecules of the fourth retardation layer, from the side closer to the fourth surface IV to the side closer to the third surface III, projected onto the fourth surface IV. That is, the orientation direction of the anisotropic molecules in the embodiment refers to the direction along the optical axis of the anisotropic molecules, from the back surface side to the observation surface side, projected onto the surface of the retardation layer. Unless otherwise specified, the orientation direction of the anisotropic molecules refers to the average orientation direction of the anisotropic molecules contained in each retardation layer.

[0057] In a plan view, the orientation direction of the first anisotropic molecules 21 and the orientation direction of the second anisotropic molecules 31 preferably differ by 180°±3°. When the orientation directions of the first anisotropic molecules 21 and the second anisotropic molecules 31 are substantially parallel and opposite to each other, a single polarizing plate louver including the first polarizer 10, the first retardation layer 20, the negative C plate 80, the second retardation layer 30, and the second polarizer 40, in this order, can be colored monochromatically when viewed from an oblique direction.

[0058] If the horizontal right direction of the above optical element when viewed from the first polarizer 10 side is defined as an azimuth angle of 0°, and if a counterclockwise angle from an azimuth angle of 0° is defined as a positive angle and a clockwise angle is defined as a negative angle, it is more preferable that the orientation direction of the first anisotropic molecules 21 is 0°±3° and the orientation direction of the second anisotropic molecules 31 is 180°±3°, or that the orientation direction of the first anisotropic molecules 21 is 180°±3° and the orientation direction of the second anisotropic molecules 31 is 0°±3°.

[0059] In plan view, it is preferable that the third anisotropic molecules 51 are oriented in a direction rotated by a predetermined angle n1 in either the clockwise or counterclockwise direction with respect to the orientation direction of the second anisotropic molecules 31, and that the fourth anisotropic molecules 61 are oriented in a direction rotated by a predetermined angle n2 in the other direction, clockwise or counterclockwise, with respect to the orientation direction of the first anisotropic molecules 21. With this configuration, the light-shielding region can be made asymmetrical in the up-down direction, i.e., the center of the light-shielding region can be shifted slightly upward or downward from the 90°-270° orientation.

[0060] In a planar view, it is more preferable that the third anisotropic molecules 51 are oriented in a direction rotated clockwise by a predetermined angle n1 with respect to the orientation direction of the second anisotropic molecules 31, and the fourth anisotropic molecules 61 are oriented in a direction rotated counterclockwise by a predetermined angle n2 with respect to the orientation direction of the first anisotropic molecules 21. By adopting such an embodiment, the center of the light-shielding region is shifted slightly upward with respect to the 90°-270° orientation, thereby making the transmittance in the upward direction higher than that in the downward direction. When the optical element is used by being overlaid on an in-vehicle display, it is preferable that the center of the light-shielding region is shifted slightly upward from the viewpoint of improving visibility. On the other hand, in a planar view, the third anisotropic molecules 51 may be oriented in a direction rotated counterclockwise by a predetermined angle n1 with respect to the orientation direction of the second anisotropic molecules 31, and the fourth anisotropic molecules 61 may be oriented in a direction rotated clockwise by a predetermined angle n2 with respect to the orientation direction of the first anisotropic molecules 21. By adopting such an embodiment, the center of the light-blocking region can be shifted slightly downward with respect to the 90°-270° azimuth, and the transmittance in the downward direction can be made higher than the transmittance in the upward direction.

[0061] The predetermined angle n1 and the predetermined angle n2 are preferably equal to or greater than 5° and equal to or less than 10°, respectively. By setting both the specified angle n1 and the specified angle n2 to 5° or more and 10° or less, the center of the shading area can be shifted slightly upward or downward relative to the 90°-270° azimuth with almost no effect on the front brightness or louver performance. The difference between the specified angle n1 and the specified angle n2 is preferably 3° or less, and more preferably they are the same. By setting the absolute value of the rotation angle n1 and the absolute value of the rotation angle n2 to be the same, the center of the shading area can be shifted slightly upward or downward while maintaining the left-right symmetry of the shading area.

[0062] From the viewpoint of preventing reflection on the windshield when the optical element is used in an in-vehicle display or the like, the absolute value of the rotation angle n1 and the absolute value of the rotation angle n2 are preferably 7° or less. From the viewpoint of further suppressing coloring in oblique directions (for example, a polar angle of 60° at an azimuth angle of 90°), the absolute value of the rotation angle n1 and the absolute value of the rotation angle n2 are preferably 6° or less.

[0063] It is preferable that the first anisotropic molecules 21 are not twisted in the thickness direction of the first retardation layer 20, the second anisotropic molecules 31 are not twisted in the thickness direction of the second retardation layer 30, the third anisotropic molecules 51 are not twisted in the thickness direction of the third retardation layer 50, and the fourth anisotropic molecules 61 are not twisted in the thickness direction of the fourth retardation layer 60.

[0064] The in-plane retardation of the first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60 is preferably 180 nm or more and 250 nm or less. By adopting such an embodiment, oblique light in the up and down directions can be more effectively suppressed. The in-plane retardation of the first to fourth retardation layers is more preferably 190 nm or more and 240 nm or less, and further preferably 200 nm or more and 230 nm or less.

[0065] Here, the first anisotropic molecules 21, the second anisotropic molecules 31, the third anisotropic molecules 51, and the fourth anisotropic molecules 61 may have positive wavelength dispersion characteristics, in which birefringence (phase difference) decreases with increasing wavelength. When anisotropic molecules with positive wavelength dispersion characteristics are used, the transmittance of the optical element 100 in oblique directions differs for each wavelength, resulting in a visual appearance of a mixture of multiple colors. One possible method for correcting this oblique coloring is to further provide a retardation layer containing anisotropic molecules with reverse wavelength dispersion characteristics, in which birefringence increases with increasing wavelength. However, anisotropic molecules with ideal wavelength dispersion characteristics capable of correcting the coloring have not yet been realized. In this embodiment, the coloring when viewed from an oblique direction is monochromatic, and by stacking retardation layers with different colors, the entire optical element 100 cancels out the color when viewed from an oblique direction, thereby correcting the color when the display device is viewed from an oblique direction. If the first polarizer 10, the first retardation layer 20, the second retardation layer 30, and the second polarizer 40 are regarded as one polarizing plate louver, and the second polarizer 40, the third retardation layer 50, the fourth retardation layer 60, and the third polarizer 70 are regarded as another polarizing plate louver, the optical element 100 can also be regarded as an optical element in which two polarizing plate louvers are stacked. For example, if the color of either one of the polarizing plate louvers is blue when viewed obliquely, the color of the other polarizing plate louver when viewed obliquely can be corrected by changing the color of the other polarizing plate louver when viewed obliquely to yellow.

[0066] The first anisotropic molecule 21, the second anisotropic molecule 31, the third anisotropic molecule 51, and the fourth anisotropic molecule 61 are molecules that cause birefringence to appear in the first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60, respectively. The anisotropic molecules are molecules that exhibit anisotropy in the refractive index of light when oriented in a specific direction. Examples of the anisotropic molecules include liquid crystal materials such as polymerizable liquid crystals and cured products of polymerizable liquid crystals. Details of polymerizable liquid crystals will be described later.

[0067] The first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60 may be, for example, reactive mesogen layers (coating retardation layers) made of a cured product of polymerizable liquid crystal (reactive mesogen). The coating retardation layers can be formed, for example, by applying a polymerizable liquid crystal to an alignment film that has been subjected to an alignment treatment and curing it by baking, light irradiation, or other methods. The cured polymerizable liquid crystal is aligned according to the alignment direction of the alignment film determined by the alignment treatment, and exhibits retardation. By adjusting the type of polymerizable liquid crystal, baking conditions, light irradiation conditions (wavelength, intensity, and irradiation angle of the irradiation light), etc., the tilt angles of the first anisotropic molecules 21, the second anisotropic molecules 31, the third anisotropic molecules 51, and the fourth anisotropic molecules 61 can be controlled and hybrid alignment can be achieved.

[0068] The alignment film used as the base of the coating retardation layer can be a film generally used in the field of liquid crystal panels, such as polyimide. The alignment treatment of the alignment film can be performed by rubbing, light irradiation, or the like.

[0069] (negative C plate) The optical element 100 has a negative C plate 80 between the first retardation layer 20 and the second retardation layer 30. By disposing the negative C plate 80 between the first retardation layer 20 and the second retardation layer 30, the orientation change of the tilt angle between the first retardation layer 20 and the second retardation layer 30 becomes more continuous. As a result, it is possible to further reduce the transmittance in the oblique direction while maintaining a high transmittance in the normal direction.

[0070] The thickness direction retardation of the negative C plate 80 is preferably 250 nm or more and 320 nm or less. By setting the thickness direction retardation to 250 nm or more and 320 nm or less, it is possible to reduce the transmittance in oblique directions in the vertical azimuth (e.g., a polar angle of 60° at an azimuth angle of 90°) and suppress color shifts at the same time. By setting the thickness direction retardation to 250 nm or more, the transmittance in oblique directions in the vertical azimuth can be set to, for example, 2% or less. By setting the thickness direction retardation to 320 nm or less, it is possible to set the chromaticity shift Δxy to, for example, 0.2 or less. Note that in this specification, the negative C plate refers to one in which nx = ny > nz, NZ = ∞.

[0071] The chromaticity shift Δxy is expressed by the following formula: In the formula, x0 and y0 are the x and y values, respectively, of the xy chromaticity diagram in the normal direction of the optical element, and x and y are the x and y values, respectively, of the xy chromaticity diagram at an arbitrary measurement point of the optical element.

[0072]

number

[0073] (Axial arrangement of each component) 4 is a diagram showing the axial orientations of the components of the optical element according to the first embodiment. As shown in FIG. 4, in a plan view, the absorption axis or reflection axis of the second polarizer 40 (hereinafter also referred to as the second absorption axis or the second reflection axis) is parallel to the absorption axis of the first polarizer 10 (hereinafter also referred to as the first absorption axis). In addition, in a plan view, the absorption axis or reflection axis of the third polarizer 70 (hereinafter also referred to as the third absorption axis or the third reflection axis) is parallel to the absorption axis of the first polarizer 10. In a plan view, the absorption axis and the transmission axis of an absorptive polarizer are orthogonal to each other, and the reflection axis and the transmission axis of a reflective polarizer are orthogonal to each other. Therefore, it can be said that the transmission axis of the first polarizer 10, the transmission axis of the second polarizer 40, and the transmission axis of the third polarizer 70 are parallel to each other. In a plan view, the slow axis of the first retardation layer 20 (hereinafter also referred to as the first slow axis) is parallel to the slow axis of the second retardation layer 30 (hereinafter also referred to as the second slow axis) and is orthogonal to the first absorption axis or the first reflection axis. By adopting such an embodiment, it is possible to suppress light leakage in oblique directions in the up and down directions, and also to suppress coloring in oblique directions.

[0074] As shown in FIG. 4 , the slow axis of the third retardation layer 50 (hereinafter also referred to as the third slow axis) and the slow axis of the fourth retardation layer 60 (hereinafter also referred to as the fourth slow axis) intersect. By intersecting the slow axis of the third retardation layer 50 and the slow axis of the fourth retardation layer 60 included in the lower-layer louver, high transmittance can be obtained in the left-right direction while making the light-shielding region asymmetrical in the up-down direction. Note that even if the slow axis of the first retardation layer 20 and the slow axis of the second retardation layer 30 included in the upper-layer louver located on the observation side intersect, sufficient transmittance cannot be obtained. Furthermore, if the retardation layers included in the upper-layer louver and the lower-layer louver are rotated one by one, the transmission region will be shifted from the center of the viewing angle, resulting in a decrease in transmittance in the normal direction, a narrower transmission region, and worsening coloring.

[0075] The angle between the slow axis of the third retardation layer 50 and the slow axis of the fourth retardation layer 60 is 10° or more and 20° or less. By setting the angle between the third slow axis and the fourth slow axis to 10° or more and 20° or less, it is possible to obtain high transmittance in the left and right azimuths while making the light-shielding region asymmetric in the vertical direction. If the angle is less than 10°, the light-shielding region cannot be made asymmetric in the vertical direction. If the angle exceeds 20°, the light-shielding region can be made asymmetric in the vertical direction, but the transmittance at the center of the viewing angle will be significantly reduced. In addition, coloring will occur in oblique directions. The angle can be adjusted to a desired angle, for example, by forming the third retardation layer 50 and the fourth retardation layer 60 separately and then rotating the third retardation layer 50 and the fourth retardation layer 60 to adjust the directions of the third slow axis and the fourth slow axis before laminating them.

[0076] From the viewpoint of preventing reflection on the windshield when the optical element is used in an in-vehicle display, etc., the angle formed by the third slow axis and the fourth slow axis is preferably 14° or less. From the viewpoint of further suppressing coloring in oblique directions (for example, a polar angle of 60° at an azimuth angle of 90°), the angle formed by the third slow axis and the fourth slow axis is preferably 12° or less.

[0077] The third and fourth slow axes are preferably not parallel to the first or second slow axis, but preferably intersect. The angle between the slow axis of the second retardation layer 30 and the slow axis of the third retardation layer 50 is preferably 5° or more and 10° or less. The angle between the slow axis of the first retardation layer 20 and the slow axis of the fourth retardation layer 60 is preferably 5° or more and 10° or less. By adopting such an embodiment, the light-shielding region can be made asymmetrical in the up and down directions while maintaining the left-right symmetry of the light-shielding region and with little effect on the front brightness and coloring in oblique directions. If the third or fourth slow axis is parallel to the first or second slow axis, the left-right symmetry may not be maintained.

[0078] Fig. 3 is an exploded plan view illustrating the slow axis of the retardation layer and the orientation direction of the anisotropic molecules. As shown in Fig. 3, the orientation of the slow axis of each retardation layer refers to the orientation along the long axis of the anisotropic molecules contained in each retardation layer in a planar view, and the tilt angle of the anisotropic molecules is not taken into consideration. In addition, the slow axis of each retardation layer is parallel to the orientation direction of the anisotropic molecules, and the orientation direction of the anisotropic molecules is not taken into consideration. For example, when the orientation direction of the first anisotropic molecule 21 and the orientation direction of the second anisotropic molecule 31 are both at an azimuth angle of 180°, when the orientation direction of the first anisotropic molecule 21 and the orientation direction of the second anisotropic molecule 31 are both at an azimuth angle of 0°, or when one of the orientation direction of the first anisotropic molecule 21 and the orientation direction of the second anisotropic molecule 31 is at an azimuth angle of 180° and the other is at an azimuth angle of 0°, the slow axis of the first retardation layer 20 and the slow axis of the second retardation layer 30 are parallel to each other in all cases.

[0079] The angle between the slow axis of the third retardation layer 50 and the slow axis of the fourth retardation layer 60 refers to the smaller angle between the two slow axes, and the orientation direction of each anisotropic molecule is not taken into consideration. For example, when one of the orientation directions of the third anisotropic molecules 51 and the fourth anisotropic molecules 61 has an azimuth angle of 10° and the other has an azimuth angle of 170°, when one has an azimuth angle of 10° and the other has an azimuth angle of 350°, when one has an azimuth angle of 190° and the other has an azimuth angle of 170°, or when one has an azimuth angle of 190° and the other has an azimuth angle of 350°, the angle between the slow axis of the third retardation layer 50 and the slow axis of the fourth retardation layer 60 is 20° in all cases.

[0080] The slow axis can be measured using a retardation measurement device (for example, "Axoscan" manufactured by Axometrics). The Axoscan can measure the retardation, slow axis, and tilt angle of anisotropic molecules. Specifically, by measuring and analyzing a 4x4 matrix (Mueller matrix) consisting of 16 elements that represent the polarization state of light, properties such as the retardation, slow axis, and tilt angle of anisotropic molecules can be measured.

[0081] When the first polarizer 10 is an absorptive polarizer, the absorption axis of the first polarizer 10 is perpendicular to the slow axis of the first retardation layer 20. When the first polarizer 10 is a laminate of an absorptive polarizer and a reflective polarizer, the absorption axis and reflection axis of the first polarizer 10 are perpendicular to the slow axis of the first retardation layer 20. In other words, the transmission axis of the first polarizer 10 and the slow axis of the first retardation layer 20 are parallel to each other.

[0082] When the second polarizer 40 is an absorptive polarizer, the second absorption axis is parallel to the first absorption axis, and when the second polarizer 40 is a reflective polarizer, the second reflection axis is parallel to the first absorption axis. When the third polarizer 70 is a reflective polarizer, the third reflection axis is parallel to the first absorption axis, and when the third polarizer 70 is a laminate of a reflective polarizer and an absorptive polarizer, the third reflection axis and the third absorption axis are parallel to the first absorption axis.

[0083] (Polymerizable liquid crystal) As the polymerizable liquid crystal, a liquid crystal polymer having a photoreactive group is preferably used. Examples of the liquid crystal polymer having a photoreactive group include a polymer having a side chain structure that combines a mesogenic group such as a biphenyl group, a terphenyl group, a naphthalene group, a phenylbenzoate group, an azobenzene group, or a derivative thereof, which is frequently used as a mesogenic component of a liquid crystal polymer, and a photoreactive group such as a cinnamoyl group, a chalcone group, a cinnamylidene group, a β-(2-phenyl)acryloyl group, a cinnamic acid group, or a derivative thereof, and having a structure such as acrylate, methacrylate, maleimide, N-phenylmaleimide, or siloxane in the main chain.

[0084] The liquid crystalline polymer may be a homopolymer consisting of a single repeating unit, or a copolymer consisting of two or more repeating units with different side chain structures. The copolymer may be any of an alternating type, a random type, a graft type, etc. Furthermore, in the copolymer, the side chain of at least one repeating unit has a structure containing both the mesogenic group and the photoreactive group, while the side chains of the other repeating units may not have the mesogenic group or the photoreactive group.

[0085] A preferred specific example of the liquid crystal polymer is a copolymerizable (meth)acrylic acid polymer having a repeating unit represented by the following general formula (I).

[0086] [ka]

[0087] In the above formula, R 1 is a hydrogen atom or a methyl group, and R 2 represents an alkyl group or a phenyl group substituted with a group selected from an alkyl group, an alkoxy group, a cyano group, and a halogen atom; ring A and ring B are each independently a group represented by the following general formulas (M1) to (M5); p and q are each independently an integer of 1 to 12; r and s are the molar fractions of each monomer in the copolymer that satisfy the relationships 0.65≦r≦0.95, 0.05≦s≦0.35, and r+s=1.

[0088] [ka]

[0089] In the above formula, X 1 ~X 38 are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, or a cyano group.

[0090] The liquid crystal polymer is preferably a copolymerizable (meth)acrylic acid polymer having a repeating unit represented by the following general formula (Ia).

[0091] [ka]

[0092] In the above formula, R 1 is a hydrogen atom or a methyl group, and R 2is an alkyl group or a phenyl group substituted with a group selected from an alkyl group, an alkoxy group, a cyano group, and a halogen atom, and X 1A ~X 4A are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, or a cyano group; ring B is a group represented by the following general formula (M1a) or (M5a); p and q are each independently an integer of 1 to 12; r and s are the molar fractions of each monomer in the copolymer that satisfy the relationships 0.65≦r≦0.95, 0.05≦s≦0.35, and r+s=1.

[0093] [ka]

[0094] In the above formula, X 1B ~X 4B and X 31B ~X 38B are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, or a cyano group.

[0095] Furthermore, the liquid crystal polymer is more preferably a copolymerizable (meth)acrylic acid polymer having a repeating unit represented by the following general formula (Ib) or (Ic).

[0096] [ka]

[0097] In the above formula, R 1 is a hydrogen atom or a methyl group, and R 2 is an alkyl group or a phenyl group substituted with a group selected from an alkyl group, an alkoxy group, a cyano group, and a halogen atom, and X 1A ~X 4A and X 31B ~X 38Bare each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, or a cyano group, p and q are each independently an integer of 1 to 12, and r and s are the molar fractions of each monomer in the copolymer that satisfy the relationships 0.65≦r≦0.95, 0.05≦s≦0.35, and r+s=1.

[0098] [ka]

[0099] In the above formula, R 1 is a hydrogen atom or a methyl group, and R 2 is an alkyl group or a phenyl group substituted with a group selected from an alkyl group, an alkoxy group, a cyano group, and a halogen atom, and X 1A ~X 4A and X 1B ~X 4B are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, or a cyano group, p and q are each independently an integer of 1 to 12, and r and s are the molar fractions of each monomer in the copolymer that satisfy the relationships 0.65≦r≦0.95, 0.05≦s≦0.35, and r+s=1.

[0100] In the above general formula (I) (including general formula (Ia), general formula (Ib) and general formula (Ic), the same applies hereinafter), R 1 R is preferably a methyl group. 2 As the substituted phenyl group, an alkyl group or a phenyl group substituted with one group selected from an alkyl group, an alkoxy group, a cyano group, and a halogen atom is preferred, and among these, a phenyl group substituted with an alkyl group, an alkoxy group, or a cyano group is more preferred, and a phenyl group substituted with an alkyl group or an alkoxy group is particularly preferred.

[0101] X 31B ~X 38B are preferably hydrogen atoms or halogen atoms, and most preferably all are hydrogen atoms.

[0102] Each of p and q is preferably an integer between 3 and 9, preferably an integer between 5 and 7, and most preferably 6. r is preferably in the range of 0.75≦r≦0.85, and most preferably 0.8. The corresponding preferred range for s is the range that is automatically determined by r+s=1. That is, it is preferably in the range of 0.15≦s≦0.25, and most preferably 0.2.

[0103] In the above general formula (Ia), (Ib) or (Ic), X 1A ~X 4A is preferably a hydrogen atom or a halogen atom, and particularly preferably X 1A ~X 4A In the general formula (Ib), it is preferable that one of X is a halogen atom and the others are hydrogen atoms, or that all of X are hydrogen atoms. 31B ~X 38B is preferably a hydrogen atom or a halogen atom, and most preferably all of them are hydrogen atoms. 1B ~X 4B is preferably a hydrogen atom or a halogen atom, and most preferably all of them are hydrogen atoms.

[0104] R 2 or R 2 The alkyl group of the substituent of the phenyl group in R is an alkyl group having 1 to 12 carbon atoms, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, and most preferably a methyl group. 2 The alkoxy group of the substituent of the phenyl group in R is an alkoxy group having 1 to 12 carbon atoms, preferably an alkoxy group having 1 to 6 carbon atoms, more preferably an alkoxy group having 1 to 4 carbon atoms, and most preferably a methoxy group. 2 Examples of the halogen atom as a substituent on the phenyl group include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and among these, a fluorine atom is preferred.

[0105] X 1 ~X38 In the above, examples of the alkyl group include those having 1 to 4 carbon atoms, of which a methyl group is most preferred; examples of the alkoxy group include those having 1 to 4 carbon atoms, of which a methoxy group is most preferred; and examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, of which a fluorine atom is preferred.

[0106] In this specification, X 1A ~X 38A is a substituent X on ring A or ring B. 1 ~X 38 and X represents a case where they are substituents on ring A. 1B ~X 38B represents the case where they are substituents on ring B. Therefore, X 1 ~X 38 The explanation about X 1A ~X 38A and X 1B ~X 38B It can also be applied to

[0107] The liquid crystalline polymer can be dissolved in a solvent to form a composition for a retardation layer. Further, the composition for a retardation layer may appropriately contain a photopolymerization initiator, a surfactant, and other components that are usually contained in a polymerizable composition that undergoes polymerization by light or heat.

[0108] Examples of the solvent used in the retardation layer composition include toluene, ethylbenzene, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, propylene glycol methyl ether, dibutyl ether, acetone, methyl ethyl ketone, ethanol, propanol, cyclohexane, cyclopentanone, methylcyclohexane, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, methoxybutyl acetate, N-methylpyrrolidone, and dimethylacetamide.

[0109] As the photopolymerization initiator, any of the commonly known general-purpose photopolymerization initiators that can form a uniform film by small amount of light irradiation can be used. Specific examples include azonitrile-based photopolymerization initiators such as 2,2'-azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile), α-aminoketone-based photopolymerization initiators such as Irgacure 907 (manufactured by Ciba Specialty Chemicals) and Irgacure 369 (manufactured by Ciba Specialty Chemicals), acetophenone-based photopolymerization initiators such as 4-phenoxydichloroacetophenone and 4-t-butyl-dichloroacetophenone, benzoin, Examples of photopolymerization initiators include benzoin-based photopolymerization initiators such as benzoin methyl ether, benzophenone-based photopolymerization initiators such as benzophenone and benzoylbenzoic acid, thioxanthone-based photopolymerization initiators such as 2-chlorothioxanthone and 2-methylthioxanthone, triazine-based photopolymerization initiators such as 2,4,6-trichloro-s-triazine and 2-phenyl-4,6-bis(trichloromethyl)-s-triazine, carbazole-based photopolymerization initiators, and imidazole-based photopolymerization initiators. Any of the photopolymerization initiators may be used alone, or two or more may be used in combination.

[0110] The surfactant may be any surfactant commonly used to form a uniform film. Specific examples include anionic surfactants such as sodium lauryl sulfate and ammonium lauryl sulfate; nonionic surfactants such as polyethylene glycol monolaurate and sorbitan stearate; cationic surfactants such as stearyl trimethylammonium chloride and behenyl trimethylammonium chloride; amphoteric surfactants such as alkyl betaines such as lauryl betaine and alkyl sulfobetaine, alkyl imidazolines, and sodium lauroyl sarcosinate; and surfactants such as BYK-361, BYK-306, and BYK-307 (manufactured by BYK Japan), Fluorad FC430 (manufactured by Sumitomo 3M), Megafac F171, and R08 (manufactured by Dainippon Ink and Chemicals, Inc.). These surfactants may be used alone or in combination of two or more.

[0111] When a liquid crystalline polymer having a photoreactive group is used as the polymerizable liquid crystal, it can be oriented by polarized light irradiation, etc., so that a coating retardation layer can be formed without providing an underlying alignment film. If a coating retardation layer is formed using a liquid crystalline polymer having a photoreactive group, the alignment film can be omitted, which enables a thinner film and a simplified manufacturing process.

[0112] (Embodiment 2) Fig. 5 is a cross-sectional schematic diagram of a display device according to embodiment 2. As shown in Fig. 5, the display device 1 according to embodiment 2 includes a liquid crystal panel 200, an optical element 100, and a backlight 300, in this order, and the optical element 100 is disposed so that the first polarizer 10 faces the liquid crystal panel 200.

[0113] Liquid crystal panel 200 may further have observation-side polarizer 400 on the observation-side side. As observation-side polarizer 400, the above-mentioned absorptive polarizer or reflective polarizer can be used, but an absorptive polarizer is preferred.

[0114] The absorption axis of the observation-side polarizer 400 and the absorption axis or reflection axis of the first polarizer 10 may be arranged perpendicular to or parallel to each other. However, from the viewpoint of obtaining high contrast, it is preferable that the absorption axis of the observation-side polarizer 400 and the absorption axis or reflection axis of the first polarizer 10 are arranged perpendicular to each other.

[0115] Typically, a liquid crystal panel has polarizers disposed on both the observation side and the back side, but it is preferable that the first polarizer 10 also serves as the polarizer disposed on the back side of the liquid crystal panel. That is, it is preferable that no other polarizers are present between the liquid crystal panel and the first polarizer 10. The first polarizer 10 may be attached to the back side of the liquid crystal panel 200, for example, with an adhesive layer or the like.

[0116] (LCD panel) The liquid crystal panel 200 may include a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates. The pair of substrates may be a TFT substrate having switching elements such as thin film transistors (TFTs) and an opposing substrate. A color filter may be provided on the TFT substrate or the opposing substrate.

[0117] The counter substrate may have, for example, color filters and a black matrix separating the color filters. The TFT substrate may have gate wiring and source wiring intersecting the gate wiring, TFTs disposed near the intersections of the gate wiring and the source wiring, and pixel electrodes electrically connected to the TFTs.

[0118] Examples of liquid crystal panels include VA (Vertical Alignment) mode, FFS (Fringe Field Switching) mode, IPS (In-Plane-Switching) mode, and TN (Twisted Nematic) mode liquid crystal panels.

[0119] In the VA mode, a counter electrode may be disposed on the CF substrate side, and the liquid crystal molecules in the liquid crystal layer may be aligned approximately perpendicular to the substrate surface when no voltage is applied to the liquid crystal layer. In the FFS and IPS modes, a counter electrode may be disposed on the TFT substrate side, and the liquid crystal molecules in the liquid crystal layer may be aligned approximately horizontally to the substrate surface when no voltage is applied. In the TN mode, a counter electrode may be disposed on the CF substrate side, and the liquid crystal molecules in the liquid crystal layer may be aligned in a helical shape by rubbing or the like, twisting from the TFT substrate toward the CF substrate. The amount of light transmission is controlled by changing the alignment of the liquid crystal molecules in response to an electric field generated in the liquid crystal layer by a voltage applied between the pixel electrode and the counter electrode. Liquid crystal panels in horizontal alignment modes such as FFS and IPS modes are preferably used because of their wide viewing angle in oblique directions.

[0120] An alignment film may be provided between each pair of substrates and the liquid crystal layer. The alignment film is a layer that has been subjected to an alignment treatment to control the alignment of liquid crystal molecules. Examples of materials for the alignment film include polymers having a main chain such as polyimide, polyamic acid, and polysiloxane, and photoalignment film materials having a photoreactive site (functional group) in the main chain or side chain are preferably used.

[0121] The liquid crystal molecules may have a positive or negative dielectric anisotropy (Δε) defined by the following formula (L): From the viewpoint of enhancing contrast, liquid crystal molecules having a negative Δε are preferred. Δε = (dielectric constant in the long axis direction) - (dielectric constant in the short axis direction) (L)

[0122] (backlight) The backlight 300 is not particularly limited as long as it irradiates light onto the liquid crystal panel 200, and may be a direct type, an edge type, or any other type. The backlight 300 may further include a light guide plate, a reflector, etc.

[0123] The backlight 300 may include an illumination unit and a prism sheet disposed on the observation surface side of the illumination unit. The illumination unit is a member that irradiates the liquid crystal panel 200 with light, and examples thereof include a cold cathode fluorescent lamp (CCFL), a light emitting diode (LED), and a light guide plate.

[0124] Fig. 6 is a perspective view showing an example of a prism sheet provided in a backlight. As shown in Fig. 6, prism sheet 301 may have multiple rows of prisms 301a extending parallel to each other on the surface on the observation side. The linear connection of the apexes of the convex portions of prisms 301a is also referred to as ridge line 301b of the prism sheet.

[0125] It is preferable that the ridge line 301b of the prism sheet 301 be arranged parallel to an azimuth angle of 0°. More specifically, the azimuth angle of the ridge line 301b is preferably 0°±3°. By arranging the ridge line 301b parallel to an azimuth angle of 0°, light collection by the prism sheet in the left-right azimuth (azimuth angle 0°-180°) is suppressed compared to the up-down azimuth (azimuth angle 90°-270°), making it possible to increase the diagonal brightness in the left-right azimuth and realize a wide viewing angle. In this case, the arrangement orientation of the prism 301a perpendicular to the ridge line 301b is an azimuth angle of 90°. This embodiment is particularly suitable for OEM standards that require a wide brightness viewing angle in the left-right azimuth.

[0126] In a plan view, the absorption axis or reflection axis of the first polarizer 10, the absorption axis or reflection axis of the second polarizer 40, and the absorption axis or reflection axis of the third polarizer 70 are preferably parallel to or perpendicular to the ridge line 301b of the prism sheet 301. By adopting such an embodiment, oblique light in the vertical direction can be more effectively suppressed.

[0127] Here, the azimuth in which side lobe light is generated varies depending on, for example, the arrangement of the ridges of the prism sheet included in the backlight. According to studies by the present inventors, it was found that when a backlight including a prism sheet 301 in which ridges 301b are arranged parallel to an azimuth angle of 0° (azimuth angle 0°-180°) or parallel to an azimuth angle of 90° (azimuth angle 90°-270°) is used, side lobe light is likely to be generated in an oblique direction in an up-down azimuth (azimuth angle 90°-270°). Therefore, by combining optical element 100 with a backlight including prism sheet 301 in which ridges 301b are arranged parallel to an azimuth angle of 0° (azimuth angle 0°-180°) or parallel to an azimuth angle of 90° (azimuth angle 90°-270°), it is possible to match the azimuth and polar angle in which side lobe light is generated with the azimuth and polar angle at which transmittance can be reduced by optical element 100, thereby effectively suppressing side lobe light.

[0128] The backlight may include a reflector on the rear side of the irradiating section. As the reflector, a metal vapor deposition film or the like that is commonly used in the field of display devices can be used. [Example]

[0129] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0130] For the optical elements of the following examples and comparative examples, the transmittance viewing angle and chromaticity transmittance viewing angle (coloring) were simulated using LCD Master and shown in contour diagrams. The circular dotted lines in the contour diagrams showing the transmittance viewing angle and chromaticity transmittance viewing angle represent polar angles of 20°, 40°, 60°, and 80° from the inside. The shading in the contour diagrams showing the transmittance viewing angle corresponds to the transmittance shown on the right side of each diagram. In the contour diagrams showing the chromaticity transmittance viewing angle, darker areas indicate that coloring was observed.

[0131] (Comparative Example 1) The optical element of Comparative Example 1 was configured to have, in order from the observation side, a first polarizer, a first retardation layer, a negative C plate, a second retardation layer, a second polarizer, a third retardation layer, a fourth retardation layer, and a third polarizer, similar to Example 1 (see FIG. 2) described later. Single-layer absorption-type linear polarizers were used as the first polarizer, the second polarizer, and the third polarizer. The negative C plate used had an Rth of 300 nm.

[0132] In Comparative Example 1, the absorption axis (first absorption axis) of the first polarizer, the absorption axis (second absorption axis) of the second polarizer, and the absorption axis (third absorption axis) of the third polarizer were arranged parallel to each other at an azimuth angle of 90°-270° in a plan view. FIG. 7 is a diagram showing the axial orientation of each member of the optical element according to Comparative Example 1. The slow axis (first slow axis) of the first retardation layer, the absorption axis (second absorption axis) of the second retardation layer, the slow axis (third slow axis) of the third retardation layer, and the absorption axis (fourth absorption axis) of the fourth retardation layer were arranged parallel to each other at an azimuth angle of 0°-180°. The axial orientation of each retardation layer shown in Table 1 below represents the orientation orientation of the anisotropic molecules contained in each retardation layer.

[0133] Table 1 below shows the tilt angles of the anisotropic molecules contained in each retardation layer. In Comparative Example 1, as in Example 1 (see FIG. 2) described later, the tilt angles of the first anisotropic molecules were hybrid-oriented so that the tilt angle continuously increased from the first polarizer 10 side of the first retardation layer 20 toward the negative C-plate 80 side, the tilt angles of the second anisotropic molecules were hybrid-oriented so that the tilt angle continuously increased from the second polarizer 40 side of the second retardation layer 30 toward the negative C-plate 80 side, the tilt angles of the third anisotropic molecules were hybrid-oriented so that the tilt angle continuously decreased from the second polarizer 40 side of the third retardation layer 50 toward the fourth retardation layer 60 side, and the tilt angles of the fourth anisotropic molecules were hybrid-oriented so that the tilt angle continuously decreased from the third polarizer 70 side toward the third retardation layer 50 side. The thicknesses of the first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60 were all the same. The in-plane retardation of each of the first retardation layer 20, the second retardation layer 30, the third retardation layer 50, and the fourth retardation layer 60 was set to 213 nm.

[0134] As in Example 1 (see FIG. 2 ) described later, the first anisotropic molecule 21 and the second anisotropic molecule 31 were configured to have symmetrical changes in tilt angle in cross-sectional view, and the third anisotropic molecule 51 and the fourth anisotropic molecule 61 were configured to have symmetrical changes in tilt angle in cross-sectional view. The tilt angle change rates of the first and second anisotropic molecules were set to be the same, and the tilt angle change rates of the third and fourth anisotropic molecules were set to be the same. The tilt angle change directions of the first anisotropic molecule 21, the second anisotropic molecule 31, the third anisotropic molecule 51, and the fourth anisotropic molecule 61 were set to be the same.

[0135] In Table 1 below, the axial arrangement of the retardation layer indicates the orientation direction (azimuth angle) of the anisotropic molecules, with the horizontal right direction when the optical element is observed from the first polarizer side being defined as an azimuth angle of 0°. The configuration of the first polarizer, first retardation layer, negative C plate, and second retardation layer is also referred to as an upper-layer louver, and the configuration of the second retardation layer, second polarizer, third retardation layer, fourth retardation layer, and third polarizer is also referred to as a lower-layer louver.

[0136] [Table 1]

[0137] Fig. 8 shows the results of a simulation of the transmittance viewing angle and coloring of the optical element of Comparative Example 1. From the results of the transmittance viewing angle in Fig. 8, it can be seen that in Comparative Example 1, the light-shielding region was symmetric (left-right symmetry) with respect to azimuth angles of 90°-270°, and light leakage in oblique directions in the up and down azimuths was suppressed, but was symmetric (up and down symmetry) with respect to azimuth angles of 0°-180° in the up and down directions. In the contour diagram showing the coloring in Fig. 8, the various colors were almost similar at the oblique directions of azimuth angles of 90° and 270°, as indicated by (i), and coloring of oblique light was suppressed.

[0138] The inventors considered that by rotating the orientation direction of the anisotropic molecules contained in each retardation layer, the symmetry of the tilt angle orientation of the anisotropic molecules would be disrupted when observed from the top and bottom directions, making the light-shielding area asymmetric. Therefore, they carried out the following study to make the light-shielding area of ​​the polarizing plate louver asymmetric from the top to the bottom.

[0139] (Comparative Examples 2 and 3) In contrast to Comparative Example 1, Comparative Example 2 had the same configuration as Comparative Example 1, except that the orientation directions of the anisotropic molecules in the first and second retardation layers included in the upper louver were rotated in the same direction (so that both rotation angles were positive). Comparative Example 3 had the same configuration as Comparative Example 1, except that the orientation directions of the anisotropic molecules in the first and second retardation layers included in the upper louver were rotated in opposite directions (so that the rotation angles were positive and negative, respectively). The orientation directions of the first to fourth anisotropic molecules are shown in Table 2 below. Note that the tilt angles of the anisotropic molecules in each retardation layer and the axial orientations of the first to third polarizers in each of the following Examples and Comparative Examples are the same as those in Comparative Example 1 and are as shown in Table 1 above, so explanations will be omitted (see Table 1).

[0140] [Table 2]

[0141] FIG. 9 shows the simulation results of the transmittance viewing angle and coloring of the optical element of Comparative Example 2. From the transmittance viewing angle results in FIG. 9, the light-shielding region of Comparative Example 2 was asymmetric in both the left-right and up-down directions. Furthermore, compared to Comparative Example 1, the maximum brightness region in the region indicated by (i) in the contour diagram showing the transmittance viewing angle was narrower and shifted from the center of the viewing angle, which suggests that it is not suitable for a polarizing plate louver. From the results of Comparative Example 2, it was found that, compared to Comparative Example 1, rotating the first and second retardation layers included in the upper-layer louver in the same direction suppressed light leakage in the up-down direction, made the light-shielding region symmetrical, and increased the transmittance at the center of the viewing angle, while maintaining the polarizing plate louver performance, and furthermore, it was not possible to make the light-shielding region asymmetrical in the up-down direction.

[0142] FIG. 10 shows the results of simulations of the transmittance viewing angle and coloring of the optical element of Comparative Example 3. The transmittance viewing angle results in FIG. 10 show that Comparative Example 3 has a light-shielding region that is symmetrical and asymmetrical in the vertical direction. However, as indicated by (i) in the contour diagram showing the transmittance viewing angle, the maximum brightness region is narrower and shifted from the center of the viewing angle compared to Comparative Example 1, making it unsuitable for a polarizing louver. The results of Comparative Example 3 indicate that rotating the first and second retardation layers included in the upper louver in opposite directions did not result in a vertically asymmetric light-shielding region while maintaining the performance of a polarizing louver. On the other hand, the light-shielding region became more vertically asymmetric than Comparative Example 2, demonstrating that rotating two adjacent retardation layers in opposite directions can make the light-shielding region vertically asymmetric.

[0143] In Comparative Examples 2 and 3, as the polar angle changed from 20° to 80° around the azimuth angle of 270° indicated by (i) in the contour diagrams showing the coloring in Figures 9 to 11, three colors of yellow, purple, and green appeared, and the coloring was intense.

[0144] (Comparative Examples 4 and 5) In Comparative Examples 4 and 5, the orientation direction of the anisotropic molecules in the retardation layer was further investigated by rotating either the retardation layer included in the upper louver or the lower louver. Comparative Examples 4 and 5 had the same configuration as Comparative Example 1, except that the orientation direction of the anisotropic molecules in either the retardation layer was rotated as shown in Table 3 below.

[0145] [Table 3]

[0146] Fig. 11 shows the results of simulations of the transmittance viewing angle and coloring of the optical element of Comparative Example 4. From the results of transmittance viewing angle in Fig. 11, it was found that in Comparative Example 4, the light-shielding region was narrowed in the vertical direction and was asymmetrical in the vertical direction, but as shown by (i) in the contour diagram showing the transmittance viewing angle, the maximum brightness region was narrower and shifted from the center of the viewing angle compared to Comparative Example 1, and therefore it was not suitable for a polarizing plate louver. The results of Comparative Example 4 showed that rotating the retardation layers included in the upper-layer louver and the lower-layer louver one by one could not make the light-shielding region asymmetric in the vertical direction while maintaining the performance as a polarizing plate louver.

[0147] Fig. 12 shows the results of simulation of the transmittance viewing angle and coloring of the optical element of Comparative Example 5. The results of transmittance viewing angle in Fig. 12 show that the light-shielding region of Comparative Example 5 is symmetrical in the left-right direction and asymmetrical in the top-bottom direction, but the maximum brightness region was narrower than that of Comparative Example 1, as shown by (i) in the contour diagram showing the transmittance viewing angle. Therefore, rotating all four retardation layers of the upper-layer louver and the lower-layer louver could not make the light-shielding region asymmetrical in the top-bottom direction while maintaining the performance of the polarizing plate louver.

[0148] In Comparative Examples 4 and 5, as the polar angle changed from 20° to 80°, three colors of yellow, purple, and green appeared near an azimuth angle of 270°, as indicated by (i) in the contour diagrams showing the coloring in Figures 11 and 12, and the coloring was intense.

[0149] (Comparative Examples 6 and 7, Examples 1 and 2) Comparative Examples 6 and 7 and Examples 1 and 2 had the same configuration as Comparative Example 1, except that the orientation direction of the anisotropic molecules in the retardation layer included in the lower louver was rotated as shown in Table 4 below.

[0150] The third anisotropic molecules were oriented in a direction rotated clockwise relative to the direction of the second anisotropic molecules, and the fourth anisotropic molecules were oriented in a direction rotated counterclockwise relative to the direction of the first anisotropic molecules. The rotation angle of the orientation direction of the third anisotropic molecules relative to the orientation direction of the second anisotropic molecules was -n°, and the rotation angle of the orientation direction of the fourth anisotropic molecules relative to the orientation direction of the first anisotropic molecules was +n°, and the absolute value n of the rotation angle is shown in the table below. The angle formed by the slow axis of the third retardation layer and the slow axis of the fourth retardation layer is twice the absolute value n of the rotation angle.

[0151] [Table 4]

[0152] FIG. 13 shows the simulation results of the transmittance viewing angle and coloring of the optical element of Example 1. From the transmittance viewing angle results in FIG. 13, the light-shielding region of Example 1 was sufficiently narrowed in the vertical direction, resulting in left-right symmetry and top-bottom asymmetricity. Furthermore, compared with Comparative Examples 2 to 5, the maximum brightness region indicated by (i) in the contour diagram showing the transmittance viewing angle was higher, resulting in a shape closer to Comparative Example 1. From the coloring results in FIG. 13, in the vertical azimuths, coloring at polar angles of 60° to 80° was almost eliminated, resulting in a color close to black. At an azimuth angle of 270°, a slight purple color appeared at polar angles of 20° to 40°, but did not appear at an azimuth angle of 90°, which is considered to be sufficient for in-vehicle use. From the results of Example 1, it was confirmed that by rotating the orientation directions of the anisotropic molecules in the two retardation layers contained in the lower louver in opposite directions, the light-shielding region could be made top-bottom asymmetric while maintaining the performance of the polarizing plate louver.

[0153] Fig. 14 shows the results of simulation of the transmittance viewing angle and coloring of the optical element of Example 2. From the results of the transmittance viewing angle in Fig. 14, it can be seen that in Example 2, the light-shielding region was sufficiently narrowed in the vertical direction, and was symmetrical left and right, and asymmetrical up and down. Compared to Example 1, the maximum brightness region of Example 2, indicated by (i) in the contour diagram showing the transmittance viewing angle, was closer to that of Comparative Example 1. Furthermore, from the results of the coloring in Fig. 14, in the vertical azimuths, the coloring at polar angles of 60° to 80° was even darker than in Example 1. Furthermore, at an azimuth angle of 270°, the purple hue at polar angles of 20° to 40° was significantly reduced compared to Example 1.

[0154] 15 shows the results of simulations of the transmittance, viewing angle, and coloring of the optical element of Comparative Example 6. The results of the transmittance and viewing angle in FIG. 15 show that, although the light-shielding region of Comparative Example 6 is symmetrical left-right and asymmetrical up-down, the maximum brightness and light-shielding performance in the vertical azimuths were significantly reduced compared to Examples 1 and 2. Furthermore, the coloring results in FIG. 15 show that intense purple and yellow coloring occurred in the vertical azimuths at polar angles of 20° to 80°. The results of Comparative Example 6 also show that even when the orientation orientations of the anisotropic molecules in the two retardation layers included in the lower-layer louver are rotated in opposite directions, the performance of the polarizing plate louver is reduced when the absolute value n of the rotation angle of the orientation orientations of the third and fourth anisotropic molecules is 20°, i.e., when the angle between the third slow axis and the fourth slow axis is 40°.

[0155] FIG. 16 shows the results of simulations of the transmittance, viewing angle, and coloring of the optical element of Comparative Example 7. The transmittance, viewing angle results in FIG. 16 show that Comparative Example 6 exhibited a decrease in front luminance, even though the light-shielding region was symmetrical and asymmetrical in the vertical direction. Furthermore, the maximum luminance was significantly reduced compared to Examples 1 and 2. As indicated by (i) in the colored contour diagram of FIG. 16, a purple hue began to appear in the shallow polar angle range of 0° to 20°, suggesting that the element is unsuitable for a polarizing plate louver. The results of Comparative Example 7 revealed that even when the orientation orientations of the anisotropic molecules in the two retardation layers included in the lower louver were rotated in opposite directions, the performance as a polarizing plate louver deteriorated when the absolute value n of the rotation angle of the orientation orientations of the third and fourth anisotropic molecules was 15°, i.e., when the angle between the third slow axis and the fourth slow axis was 30°.

[0156] From the results of Examples 1 and 2 and Comparative Examples 6 and 7, it was found that by setting the rotation angles of the orientation directions of the third and fourth anisotropic molecules to 10° or less, respectively, i.e., by setting the angle between the third slow axis and the fourth slow axis to 20° or less, it is possible to maintain the performance of the polarizing plate louver while further making the shading area asymmetric in the upper and lower directions.

[0157] (Consideration of transmittance and chromaticity shift Δxy) FIG. 17 is a graph showing the transmittance of the optical element of Comparative Example 1. FIG. 18 is a graph showing the transmittance of the optical element of Example 1. FIG. 19 is a graph showing the transmittance of the optical element of Example 2. The horizontal axis of each graph represents the polar angle, and the vertical axis represents the transmittance (%). The graphs in FIGS. 17 to 19 correspond to the transmittance of the optical element when the polar angle is changed from an azimuth angle of 90° to 270° in the contour diagrams showing the transmittance viewing angles in FIGS. 8, 13, and 14, respectively. In FIGS. 17 to 19, the normal direction is set to 0°, and an azimuth angle of 90° is expressed as a positive value and an azimuth angle of 270° is expressed as a negative value.

[0158] Table 5 below summarizes the maximum transmittance of the graph for Comparative Example 1 shown in FIG. 17, the maximum transmittance of the graph for Example 1 shown in FIG. 18, and the maximum transmittance of the graph for Example 2 shown in FIG. 19. Table 5 also summarizes the chromaticity shift Δxy values ​​for Comparative Example 1, Examples 1, and 2 at a polar angle of 60° at an azimuth angle of 90°. The chromaticity shift Δxy is expressed by the following formula. In the formula below, x0 and y0 are the x and xy values ​​in the xy chromaticity diagram in the normal direction of the optical element, respectively. Calculations were performed using the x and y values ​​in the xy chromaticity diagram for Comparative Example 1, Example 1, and Example 2 at an azimuth angle of 90° and a polar angle of 60° as x and y in the formula below, respectively. The smaller the Δxy value, the closer the appearance to achromatic color (black), indicating an improved color tone. When an optical element is used for vehicle installation, the user often observes the optical element from above (diagonal direction between azimuth angles of 0° and 90°), and the bottom side of the optical element (diagonal direction between azimuth angles of 0° and 270°) is almost invisible to the user. For this reason, we investigated Δxy at a polar angle of 60° at an azimuth angle of 90°.

[0159]

number

[0160] [Table 5]

[0161] As shown in Table 5, the maximum transmittance of Comparative Example 1 was 35.1%, that of Example 1 was 31.6%, and that of Example 2 was 34.0%. As shown in FIG. 17, the maximum brightness (peak top) of Comparative Example 1 was at a polar angle of 0° (normal direction), and the transmittance graph was nearly symmetrical about a polar angle of 0°, symmetrical between the upward direction (azimuth angle 90°) where the polar angle was expressed as a positive value and the downward direction (azimuth angle 270°) where the polar angle was expressed as a negative value. On the other hand, as shown in FIGS. 18 and 19, the peak top of Example 1 was at a polar angle of 15°, and the peak top of Example 2 was at a polar angle of 10°. Since the peak tops were shifted upward from the normal direction, the transmittance was higher on the upper side than on the lower side, confirming the vertical asymmetry. Note that when Δxy is 0.06 or less, the color cannot be distinguished with the naked eye, and therefore, coloring was hardly visible in Examples 1 and 2.

[0162] <Consideration of the rotation angle range> (Comparative Example 8, Example 3) The rotation angle was changed to 0, 3, 5, 7, and 10°, and the maximum transmittance, the transmittance at a polar angle of 60° at an azimuth angle of 90°, and Δxy were investigated. Comparative Example 8 and Example 3 had the same configuration as Comparative Example 1, except that the orientation direction of the anisotropic molecules in the retardation layer included in the lower-layer louver was rotated as shown in Table 6 below.

[0163] [Table 6]

[0164] Fig. 20 shows the results of a simulation of the transmittance viewing angle of the optical element of Comparative Example 8. As shown in Fig. 20, in Comparative Example 8 where the rotation angle n is 3°, the light blocking region is symmetrical in the vertical direction.

[0165] FIG. 21 is a graph showing the relationship between the rotation angle of the orientation direction of the anisotropic molecules and the maximum transmittance relative ratio. The transmittance relative ratio represents the relative ratio of the maximum transmittance of each Example and Comparative Example, with the maximum transmittance of Comparative Example 1 being 100%. When the maximum transmittance relative ratio is ±10%, it can be said that the transmittance is sufficiently high. In FIG. 21, the preferred range is shaded. It was found from FIG. 20 that high transmittance can be maintained in the left and right directions within the range of rotation angle n = 0° to 10°. It was also found that the maximum transmittance tends to decrease as the rotation angle increases.

[0166] According to the inventors' investigations, when an optical element is used in an in-vehicle display, the display is positioned slightly below the driver's line of sight, and the driver is actually viewing the upper half of the display at polar angles between 20° and 60°. Therefore, with a standard optical element, display light from polar angles greater than 60° may be reflected on the windshield. Therefore, the transmittance at a polar angle of 60° at an azimuth angle of 90° was investigated. Figure 22 is a graph showing the relationship between the rotation angle of the orientation orientation of the anisotropic molecules and the transmittance at a polar angle of 60° at an azimuth angle of 90°. In Figure 22, the preferred range is shaded. It was found from Figure 22 that the greater the absolute value n of the rotation angle, the lower the oblique light blocking effect tends to be. When the transmittance at a polar angle of 60° at an azimuth angle of 90° exceeds 2.0%, reflections on the windshield are more likely to occur. Considering reflection on the windshield, the transmittance at an azimuth angle of 90° and a polar angle of 60° is preferably 2.0% or less, and the rotation angle n is preferably 7° or less. In addition, the angle formed by the slow axis of the third retardation layer and the slow axis of the fourth retardation layer is preferably 14° or less.

[0167] FIG. 23 is a graph showing the relationship between the rotation angle of the orientation direction of anisotropic molecules and Δxy. From FIG. 23, it was found that the larger the absolute value n of the rotation angle, the more likely coloring occurs in oblique directions. In FIG. 23, the preferred range is shaded. When Δxy at a polar angle of 60° at an azimuth angle of 90° exceeds 0.06, coloring becomes more visible. Therefore, from the perspective of suppressing coloring, Δxy at a polar angle of 60° at an azimuth angle of 90° is particularly preferably 0.06 or less, and the rotation angle n is preferably 6° or less. Considering both the light blocking rate and coloring, it was found that an excellent louver and characteristics can be obtained by setting the rotation angle n to 6° or less. Since the rotation angle n is preferably 6° or less, the angle between the slow axis of the third retardation layer and the slow axis of the fourth retardation layer is preferably 12° or less. In Example 3 and Comparative Example 8, Δxy was 0.06 or less, and coloring was almost invisible to the naked eye.

[0168] (Examples 1 to 3) The relationship between the phase difference of the negative C plate and the transmittance in an oblique direction was investigated below. Optical elements of Investigation Examples 1 to 3 were fabricated in the same manner as Comparative Example 1, except that the phase difference of the negative C plate was changed to 100 nm, 200 nm, and 400 nm, respectively. Table 7 below summarizes the transmittance at an azimuth angle of 90° and a polar angle of 60°.

[0169] [Table 7]

[0170] As shown in Table 7, it was confirmed that when the phase difference of the negative C plate is 300 nm or more, the transmittance in the oblique direction decreases to about 1%.

[0171] FIG. 24 is a graph showing the relationship between thickness direction retardation and transmittance of a negative C plate. FIG. 25 is a graph showing the relationship between thickness direction retardation and Δxy of a negative C plate. It is preferable that the polarizing plate louver have a transmittance of 2.0% or less at a polar angle of 60° at an azimuth angle of 90° and a chromaticity shift Δxy of 0.2 or less at a polar angle of 60° at an azimuth angle of 90°. As shown in FIG. 24, when the thickness direction retardation of the negative C plate was approximately 250 nm or more, the transmittance of 2% or less at a polar angle of 60° at an azimuth angle of 90°. As shown in FIG. 25, when the thickness direction retardation of the negative C plate was approximately 320 nm or less, the chromaticity shift Δxy of 0.2 or less. From these results, it is preferable that the thickness direction retardation of the negative C plate be 250 nm or more and 320 nm or less. [Explanation of symbols]

[0172] 1:Display device 10:First polarizer 20: First retardation layer 21, 21A, 21B: First anisotropic molecule 30:Second retardation layer 31, 31A, 31B: Second anisotropic molecule 40:Second polarizer 50:Third retardation layer 51, 51A, 51B: Third anisotropic molecule 60: Fourth retardation layer 61, 61A, 61B: Quaternary anisotropic molecules 70: Third polarizer 80: Negative C plate 100, 1001: Optical elements 200: LCD panel 300: Backlight 301: Prism sheet 301a: Prism 301b: Ridgeline 400: Observation side polarizer

Claims

1. a first polarizer, a first retardation layer containing first anisotropic molecules, a negative C plate, a second retardation layer containing second anisotropic molecules, a second polarizer, a third retardation layer containing third anisotropic molecules, a fourth retardation layer containing fourth anisotropic molecules, and a third polarizer, in this order; the first anisotropic molecules change so that a tilt angle thereof increases from the first polarizer side toward the negative C plate side of the first retardation layer, the second anisotropic molecules change so that a tilt angle thereof increases from the second polarizer side toward the negative C plate side of the second retardation layer, the third anisotropic molecules change so that a tilt angle becomes smaller from the second polarizer side of the third retardation layer toward the fourth retardation layer side, the fourth anisotropic molecules change so that a tilt angle becomes smaller from the third polarizer side toward the third retardation layer side of the fourth retardation layer, an absorption axis or a reflection axis of the first polarizer, an absorption axis or a reflection axis of the second polarizer, and an absorption axis or a reflection axis of the third polarizer are parallel to one another in a plan view; In a plan view, an absorption axis or a reflection axis of the first polarizer and a slow axis of the first retardation layer are perpendicular to each other, In a plan view, the slow axis of the first retardation layer and the slow axis of the second retardation layer are parallel to each other, In a plan view, the slow axis of the third retardation layer and the slow axis of the fourth retardation layer intersect with each other, an angle formed between the slow axis of the third retardation layer and the slow axis of the fourth retardation layer is 10° or more and 20° or less.

2. an angle formed between the slow axis of the second retardation layer and the slow axis of the third retardation layer is 5° or more and 10° or less; 2 . The optical element according to claim 1 , wherein an angle formed between the slow axis of the first retardation layer and the slow axis of the fourth retardation layer is 5° or more and 10° or less.

3. a surface of the first retardation layer on the first polarizer side is a first surface, a surface of the second retardation layer on the second polarizer side is a second surface, a surface of the third retardation layer on the second polarizer side is a third surface, and a surface of the fourth retardation layer on the third polarizer side is a fourth surface, a direction along the major axis of the first anisotropic molecules projected onto the first surface from a side closer to the second surface of the first retardation layer to a side closer to the first surface is defined as an orientation direction of the first anisotropic molecules; a direction along the long axis of the second anisotropic molecules projected onto the second surface from a side closer to the second surface of the second retardation layer to a side closer to the first surface is defined as an orientation direction of the second anisotropic molecules; a direction along the major axis of the third anisotropic molecules projected onto the third surface from a side closer to the fourth surface of the third retardation layer to a side closer to the third surface is defined as an orientation direction of the third anisotropic molecules; When a direction along the long axis of the fourth anisotropic molecules from a side closer to the fourth surface of the fourth retardation layer to a side closer to the third surface is projected onto the fourth surface, the direction is defined as an orientation direction of the fourth anisotropic molecules, The optical element according to claim 1 , wherein, in a plan view, the alignment direction of the first anisotropic molecules and the alignment direction of the second anisotropic molecules differ by 180°±3°.

4. When the horizontal right direction of the optical element viewed from the first polarizer side is defined as an azimuth angle of 0°, and a counterclockwise direction from the azimuth angle of 0° is defined as a positive angle, and a clockwise direction from the azimuth angle of 0° is defined as a negative angle, The orientation of the first anisotropic molecules is 0°±3° and the orientation of the second anisotropic molecules is 180°±3°, or The optical element according to claim 3 , wherein the orientation direction of the first anisotropic molecules is 180°±3°, and the orientation direction of the second anisotropic molecules is 0°±3°.

5. In a plan view, the orientation direction of the third anisotropic molecules is an orientation rotated by a predetermined angle in either a clockwise or counterclockwise direction with respect to the orientation direction of the second anisotropic molecules, The optical element described in claim 3, wherein, in a planar view, the orientation direction of the fourth anisotropic molecules is an orientation rotated by the predetermined angle in the other direction of the clockwise and counterclockwise directions relative to the orientation direction of the first anisotropic molecules.

6. The optical element according to claim 5 , wherein the predetermined angle is equal to or greater than 5° and equal to or less than 10°.

7. 2. The optical element according to claim 1, wherein the retardation in the thickness direction of the negative C plate is 250 nm or more and 320 nm or less.

8. 2. The optical element according to claim 1, wherein a rate of change in the tilt angle of the first anisotropic molecules from the first polarizer side to the negative C plate side along the thickness direction of the first retardation layer is the same as a rate of change in the tilt angle of the second anisotropic molecules from the second polarizer side to the negative C plate side along the thickness direction of the second retardation layer.

9. 2. The optical element according to claim 1, wherein the rate of change in the tilt angle of the third anisotropic molecule from the fourth retardation layer side to the second polarizer side along the thickness direction of the third retardation layer is the same as the rate of change in the tilt angle of the fourth anisotropic molecule from the third retardation layer side to the third polarizer side along the thickness direction of the fourth retardation layer.

10. the first polarizer is an absorptive polarizer, a reflective polarizer, or a laminate of an absorptive polarizer and a reflective polarizer, the second polarizer is an absorptive polarizer or a reflective polarizer, The optical element according to claim 1 , wherein the third polarizer is an absorptive polarizer, a reflective polarizer, or a laminate of an absorptive polarizer and a reflective polarizer.

11. A liquid crystal panel, an optical element according to any one of claims 1 to 10, and a backlight are provided in this order, The display device, wherein the optical element is disposed so that the first polarizer faces the liquid crystal panel.

12. the backlight includes an illumination unit and a prism sheet disposed on the observation surface side of the illumination unit; the prism sheet has a plurality of rows of linear convex portions extending parallel to one another on the surface on the observation side; The display device according to claim 11 , wherein, in a plan view, the absorption axis of the first polarizer is parallel to or perpendicular to the ridge lines of the linear convex portions.

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