Optical element and display device

Abstract

To provide an optical element that can suppress light leakage in an oblique direction vertically and suppress coloring in the oblique direction, and a display device.SOLUTION: An optical element includes a first polarizer, first and second retardation layers, a second polarizer, third and fourth retardation layers, and a third polarizer in this order. Absorption axes or reflection axes of the first, second, and third polarizers are parallel to each other, slow axes of the first and second retardation layers are parallel to each other, slow axes of the third and fourth retardation layers are parallel to each other, the absorption axis or the reflection axis of the first polarizer and the slow axis of the first retardation layer are orthogonal to each other. Tilt angles of first anisotropic molecules become larger from the first polarizer side toward the second retardation layer side, and tilt angles of second anisotropic molecules become larger from the second polarizer side toward the first retardation layer 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.SELECTED DRAWING: Figure 2A

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, according to the inventors' investigations, when viewed from an oblique direction, the displayed image may be colored in an unintended color, so there is 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 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 and suppress coloring in diagonal directions, and a display device that is 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 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, in a planar view, 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 planar view, a slow axis of the first retardation layer and a slow axis of the second retardation layer are parallel to one another, in a planar view, a slow axis of the third retardation layer and a slow axis of the fourth retardation layer are parallel to one another, and in a planar view, an absorption axis or a reflection axis of a polarizer and a slow axis of the first retardation layer are orthogonal to each other; the first anisotropic molecule changes so that its tilt angle becomes larger from the first polarizer side of the first retardation layer toward the second retardation layer side; the second anisotropic molecule changes so that its tilt angle becomes larger from the second polarizer side of the second retardation layer toward the first retardation layer side; the third anisotropic molecule changes so that its tilt angle becomes smaller from the second polarizer side of the third retardation layer toward the fourth retardation layer side; and the fourth anisotropic molecule changes so that its tilt angle becomes smaller from the third polarizer side of the fourth retardation layer toward the third retardation layer side.

[0011] (2) In an embodiment of the present invention, in addition to the configuration of (1), 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 of the first retardation layer from a side closer to the second surface to a side closer to the first surface, projected onto the first surface, is an orientation direction of the first anisotropic molecules, and a direction along the major axis of the second anisotropic molecules of the second retardation layer from a side closer to the second surface to a side closer to the first surface, projected onto the second surface, is an orientation direction of the second anisotropic molecules. the orientation direction of the third anisotropic molecule is defined as the orientation direction of the third anisotropic molecule, 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 toward the side closer to the third surface is defined as the orientation direction of the third anisotropic molecule, and 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 toward the side closer to the third surface is defined as the orientation direction of the fourth anisotropic molecule, when viewed in a plane, the orientation direction of the first anisotropic molecule and the orientation direction of the second anisotropic molecule differ by 180°±3°, and the orientation direction of the third anisotropic molecule and the orientation direction of the fourth anisotropic molecule differ by 180°±3°.

[0012] (3) In one embodiment of the present invention, in addition to the configuration of (1) or (2) above, the horizontal right direction of the optical element as viewed 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 direction of each of the first anisotropic molecule and the fourth anisotropic molecule is 0°±3°, and the orientation direction of each of the second anisotropic molecule and the third anisotropic molecule is 180°±3°, or the orientation direction of each of the first anisotropic molecule and the fourth anisotropic molecule is 180°±3°, and the orientation direction of each of the second anisotropic molecule and the third anisotropic molecule is 0°±3°.

[0013] (4) An embodiment of the present invention is an optical element having any one of the configurations (1) to (3) above, further comprising a negative C plate between the first retardation layer and the second retardation layer.

[0014] (5) An embodiment of the present invention is an optical element having the configuration of (4) above, wherein the retardation in the thickness direction of the negative C plate is 250 nm or more and 320 nm or less.

[0015] (6) An embodiment of the present invention is an optical element having any one of the configurations (1) to (5) above, wherein, in plan view, the slow axis of the third retardation layer and the slow axis of the fourth retardation layer are parallel to the slow axis of the first retardation layer.

[0016] (7) An embodiment of the present invention is an optical element having any one of the configurations (1) to (6) above, wherein a rate of change in the tilt angle of the first anisotropic molecule from the first polarizer side to the second retardation layer 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 molecule from the second polarizer side to the first retardation layer side along the thickness direction of the second retardation layer.

[0017] (8) An 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 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.

[0018] (9) In one embodiment of the present invention, in addition to the configuration of any one of (1) to (8) above, 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.

[0019] (10) Another embodiment of the present invention is a display device comprising a liquid crystal panel, an optical element according to any one of (1) to (9) above, and a backlight, in this order, wherein the optical element is positioned so that the first polarizer faces the liquid crystal panel.

[0020] (11) In one embodiment of the present invention, in addition to the configuration of (10), 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 the absorption axis of the first polarizer is parallel to or perpendicular to the ridge line of the linear convex portions in a planar view. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide an optical element that can suppress light leakage in oblique directions in the vertical direction and suppress coloring in oblique directions, and a display device that includes the optical element. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2 is a diagram illustrating a polar angle and an azimuthal angle. [Figure 2A] 1 is a cross-sectional view schematically illustrating an optical element according to a first embodiment. [Figure 2B] FIG. 2 is an exploded perspective view illustrating the slow axis of each retardation layer and the orientation direction of anisotropic molecules. [Figure 3] 3 is a diagram showing the axial orientations of the components of the optical element according to the first embodiment. FIG. [Figure 4] FIG. 4 is a cross-sectional view schematically illustrating an optical element according to a second embodiment. [Figure 5] FIG. 10 is a cross-sectional view illustrating a display device according to a third embodiment. [Figure 6] FIG. 2 is a perspective view showing an example of a prism sheet provided in the backlight. [Figure 7] FIG. 2 is a cross-sectional view schematically illustrating an optical element of Comparative Example 1. [Figure 8] 10 is a diagram showing the axial orientations of the members of the optical element of Comparative Example 1. FIG. [Figure 9] FIG. 10 is a cross-sectional view schematically illustrating an optical element of Comparative Example 2. [Figure 10] FIG. 10 is a cross-sectional view schematically illustrating an optical element of Comparative Example 3. [Figure 11] 10 is a cross-sectional schematic view of an optical element of Comparative Example 4. [Figure 12] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 1. [Figure 13] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 2. [Figure 14] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 3. [Figure 15] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Comparative Example 4. [Figure 16] 1 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Example 1. [Figure 17] 10 shows simulation results of transmittance, viewing angle, and coloring of the optical element of Example 2. [Figure 18] 1 is a graph in which the transmittances of Comparative Example 2, Example 1, and Example 2 are superimposed. [Figure 19] FIG. 10 is a cross-sectional view schematically illustrating an optical element of Comparative Example 5. [Figure 20] FIG. 10 is a diagram showing the axial orientations of the members of the optical element of Comparative Example 5. [Figure 21] 10 shows the results of simulation of the transmittance, viewing angle, and coloring of the optical element of Comparative Example 5. [Figure 22] 10 is a graph showing the relationship between the retardation and transmittance in the thickness direction of a negative C plate. [Figure 23] 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

[0023] 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.

[0024] [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.

[0025] 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.

[0026] 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=(nx-ny)×d Rth={nz-(nx+ny) / 2}×d NZ=(ns-nz) / (ns-nf)

[0027] "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.

[0028] 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.

[0029] (Embodiment 1) 2A is a cross-sectional schematic diagram of an optical element according to embodiment 1. As shown in FIG. 2A, an optical element 100A according to embodiment 1 includes a first polarizer 10, a first retardation layer 20, 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 100A 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. If a configuration including the first polarizer 10, the first retardation layer 20, 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 100A 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 100A 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 100A 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.

[0030] (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.

[0031] 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 100A, side lobe light can be absorbed, and the light blocking properties in oblique directions in the vertical direction can be further improved.

[0032] 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 100A, 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] (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.

[0038] As shown in FIG. 2A , 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 second retardation layer 30 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 first retardation layer 20 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.

[0039] 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, and the first anisotropic molecules located on the second retardation layer 30 side of the first retardation layer 20 are referred to as first anisotropic molecules 21B. The tilt angle of the first anisotropic molecules 21A is 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 second 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 first retardation layer 20 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 3-2Of 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.

[0040] 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.

[0041] 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.

[0042] As shown in FIG. 2A, the 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 4-2It 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, with different tilt angles 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, which will be described later, it is possible to make the color of the optical element 100A when viewed from an oblique direction nearly monochrome.

[0043] In the first embodiment, the first retardation layer 20 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.

[0044] It is preferable that the change in tilt angle of the first anisotropic molecule 21 and the second anisotropic molecule 31 is symmetrical in cross section. The rate of change in the tilt angle of the first anisotropic molecule 21, which changes from the first polarizer 10 side to the second retardation layer 30 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 molecule 31, which changes from the second polarizer 40 side to the first retardation layer 20 side along the thickness direction of the second retardation layer 30. The rate of change in the tilt angle of the first anisotropic molecule can be expressed by the following formula (1), and the rate of change in the tilt angle of the second anisotropic molecule 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)

[0045] It is preferable that the change in tilt angle of the third anisotropic molecule 51 and the fourth anisotropic molecule 61 is symmetrical in cross section. The rate of change in the tilt angle of the third anisotropic molecule 51 from the fourth retardation layer 60 side to the second polarizer 40 side along the thickness direction of the third retardation layer 50 is the same as the rate of change in the tilt angle of the fourth anisotropic molecule 61 from the third retardation layer 50 side to the third polarizer 70 side along the thickness direction of the fourth retardation layer 60. 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)

[0046] 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.

[0047] 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.

[0048] The direction of change in the tilt angle of the anisotropic molecules refers to the direction in which the long axes of the anisotropic molecules rise (the tilt angle increases). Specifically, the direction of change in the tilt angle of the anisotropic molecules refers to the direction along the long axes of the anisotropic molecules projected onto the one surface from the side closer to one surface of the retardation layer 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 which the anisotropic molecules have a smaller tilt angle, and the other surface can be said to be the surface on which the anisotropic molecules have a larger tilt angle. In cross-sectional views (such as FIG. 2A), the direction of change in the tilt angle of the anisotropic molecules is indicated by the direction of the outline 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 second polarizer 40 (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.

[0049] 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.

[0050] 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.

[0051] 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, 1-2and the above θ 2-2 It is more preferable that the above formulas are the same as those of the formulas.

[0052] 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.

[0053] 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.

[0054] 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 4-2 It is more preferable that the above formulas are the same as those of the formulas.

[0055] In a planar 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°. Furthermore, in a planar view, the orientation direction of the third anisotropic molecules 51 and the orientation direction of the fourth anisotropic molecules 61 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, one polarizing plate louver including the first polarizer 10, the first retardation layer 20, the second retardation layer 30, and the second polarizer 40 in this order can be colored monochromatically when viewed obliquely. Furthermore, when the orientation directions of the third anisotropic molecules 51 and the fourth anisotropic molecules 61 are substantially parallel and opposite to each other, another polarizing plate louver including the second polarizer 40, the third retardation layer 50, the fourth retardation layer 60, and the third polarizer 70 in this order can be colored monochromatically when viewed obliquely. For example, if the color of either one of the polarizing plate louvers is blue when viewed from an oblique direction, by making the color of the other polarizing plate louver yellow when viewed from an oblique direction and stacking the two polarizing plate louvers, the coloring when viewed from an oblique direction is canceled out, and the color of the entire optical element 100A when viewed from an oblique direction can be corrected.

[0056] The orientation direction of the anisotropic molecules will be described below. As shown in FIG. 2A, the surface of the first retardation layer 20 facing the first polarizer 10 is referred to as the first surface I, the surface of the second retardation layer 30 facing the second polarizer 40 is referred to as the second surface II, the surface of the third retardation layer 50 facing the second polarizer 40 is referred to as the third surface III, and the surface of the fourth retardation layer 60 facing the third polarizer 70 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 projected onto the first surface I from the side closer to the second surface II of the first retardation layer toward the side closer to the first surface. The orientation direction of the second anisotropic molecules refers to the direction along the major axis of the second anisotropic molecules projected onto the second surface II from the side closer to the second surface II of the second retardation layer toward the side closer to the first surface I. 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] If the horizontal right direction of the optical element as seen from the first polarizer 10 side is defined as an azimuth angle of 0°, and 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 preferable that the orientation direction of each of the first anisotropic molecule and the fourth anisotropic molecule is 0°±3°, and that the orientation direction of each of the second anisotropic molecule and the third anisotropic molecule is 180°±3°. Alternatively, it is preferable that the orientation direction of each of the first anisotropic molecule and the fourth anisotropic molecule is 180°±3°, and that the orientation direction of each of the second anisotropic molecule and the third anisotropic molecule is 0°±3°.

[0058] 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.

[0059] 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.

[0060] 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 100A in oblique directions varies with 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 100A cancels out the color when viewed from an oblique direction, thereby correcting the color when the display device is viewed from an oblique direction.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] (Axial arrangement of each component) 3 is a diagram showing the axial orientations of each member of the optical element according to the first embodiment. As shown in FIG. 3, 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.

[0065] In plan view, 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) are preferably parallel to each other and also parallel to the first slow axis. That is, in plan view, the first slow axis, the second slow axis, the third slow axis, and the fourth slow axis are preferably parallel to each other.

[0066] FIG. 2B is an exploded perspective view illustrating the slow axis of each retardation layer and the orientation direction of the anisotropic molecules. As shown in FIG. 2B, 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, without taking into account the tilt angle and orientation direction of the anisotropic molecules. The slow axis of each retardation layer is parallel to the orientation direction of the anisotropic molecules. For example, the slow axes of multiple retardation layers whose anisotropic molecule orientation directions are 180° azimuth angle are parallel to each other. The slow axes of multiple retardation layers whose anisotropic molecule orientation directions are 0° azimuth angle are parallel to each other. Furthermore, the slow axis of a retardation layer whose anisotropic molecule orientation direction is 180° azimuth angle is parallel to the slow axis of a retardation layer whose anisotropic molecule orientation direction is 0° azimuth angle is also parallel to each other.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] (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.

[0071] 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.

[0072] 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).

[0073] [ka]

[0074] 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.

[0075] [ka]

[0076] 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.

[0077] The liquid crystal polymer is preferably a copolymerizable (meth)acrylic acid polymer having a repeating unit represented by the following general formula (Ia).

[0078] [ka]

[0079] 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 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.

[0080] [ka]

[0081] 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.

[0082] 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).

[0083] [ka]

[0084] 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 38B 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.

[0085] [ka]

[0086] 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.

[0087] 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. 2As 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.

[0088] X 31B ~X 38B are preferably hydrogen atoms or halogen atoms, and most preferably all are hydrogen atoms.

[0089] 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.

[0090] 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.

[0091] R 2 or an alkyl group of R 2The 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.

[0092] X 1 ~X 38 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.

[0093] 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

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] (Embodiment 2) Fig. 4 is a cross-sectional schematic diagram of an optical element according to embodiment 2. As shown in Fig. 4, the optical element 100B according to embodiment 2 has the same configuration as that of embodiment 1 except that it has a negative C plate 80 between the first retardation layer 20 and the second retardation layer 30, and therefore a duplicated description will be omitted. 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 oblique directions while maintaining a high transmittance in the normal direction.

[0100] In the second embodiment, the first retardation layer 20 and the second retardation layer 30 may each be in contact with the negative C plate 80. Furthermore, the third retardation layer 50 and the fourth retardation layer 60 may be in contact with each other.

[0101] 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., azimuth angle 90°, polar angle 60°) and suppress color shifts. 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. In this specification, the negative C plate refers to one in which nx = ny > nz, NZ = ∞.

[0102] 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.

[0103]

number

[0104] The optical element 100B of the second embodiment can also suppress light leakage in oblique directions in the up and down directions, and can also suppress coloring in oblique directions.

[0105] (Embodiment 3) Fig. 5 is a cross-sectional schematic diagram of a display device according to embodiment 3. As shown in Fig. 5, the display device 1 according to embodiment 3 includes a liquid crystal panel 200, an optical element 100A, and a backlight 300, in this order, and the optical element 100A is disposed so that the first polarizer 10 faces the liquid crystal panel 200. Fig. 5 illustrates the case where the optical element 100A of embodiment 1 is used as the optical element, but the optical element 100B of embodiment 2 may also be used.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] (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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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)

[0115] (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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] Here, the direction in which the side lobe light is generated varies depending on, for example, the arrangement of the ridges of the prism sheet provided in the backlight. According to studies by the present inventors, it was found that when a backlight is used that includes 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°), side lobe light is likely to be generated in an oblique direction in the up and down azimuth (azimuth angle 90°-270°). Therefore, by combining optical element 100A of embodiment 1 or optical element 100B of embodiment 2 with a backlight having a prism sheet 301 in which ridge line 301b is 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 becomes possible to match the azimuth and polar angle at which side lobe light is generated with the azimuth and polar angle at which transmittance can be reduced by optical element 100, and side lobe light can be effectively suppressed.

[0121] 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]

[0122] 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.

[0123] 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 of 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 of transmittance viewing angle corresponds to the transmittance shown on the right side of each diagram. In the contour diagrams of chromaticity transmittance viewing angle, darker areas indicate that coloring was observed.

[0124] (Comparative Example 1) 7 is a cross-sectional schematic diagram of the optical element of Comparative Example 1. As shown in FIG. 7, the optical element 1001 of Comparative Example 1 has, in order from the observation side, a first polarizer 10, a first retardation layer 20, a second retardation layer 30, and a second polarizer 40. In Comparative Example 1, θ 1-1 = 70°, θ 1-2 = 4°, θ 2-1 = 4°, θ 2-2 =70°.

[0125] Fig. 8 is a diagram showing the axial orientations of each member of the optical element of Comparative Example 1. In Comparative Example 1, single-layer absorbing linear polarizers were used as the first polarizer and the second polarizer. As shown in Fig. 8, in Comparative Example 1, the first polarizer and the second polarizer were arranged parallel to each other at an azimuth angle of 90°-270° so that their absorption axes (first absorption axis) were parallel to each other in a plan view. The slow axis (first slow axis) of the first retardation layer and the slow axis (second slow axis) of the second retardation layer were arranged parallel to each other at an azimuth angle of 0°-180° so that their absorption axes (first absorption axis) were parallel to each other.

[0126] As shown in FIG. 7 , in the first retardation layer 20, the tilt angles of the first anisotropic molecules were hybrid-aligned so that the tilt angles continuously decreased from the first polarizer 10 side of the first retardation layer 20 toward the second retardation layer 30 side. In the second retardation layer 30, the tilt angles of the second anisotropic molecules were hybrid-aligned so that the tilt angles continuously increased from the second polarizer 40 side of the second retardation layer 30 toward the first retardation layer 20 side. The thickness of the first retardation layer 20 and the thickness of the second retardation layer 30 were made the same. In addition, the alignment direction of the first anisotropic molecules 21 was set to an azimuth angle of 0°, and the alignment direction of the second anisotropic molecules 31 was set to an azimuth angle of 180°.

[0127] The changes in the tilt angles of the first anisotropic molecules 21 and the second anisotropic molecules 31 were made asymmetric with respect to the interface between the first retardation layer 20 and the second retardation layer 30. In addition, the change direction of the tilt angle of the first anisotropic molecules 21 and the change direction of the tilt angle of the second anisotropic molecules 31 (white arrows in each retardation layer in FIG. 7) were made opposite to each other.

[0128] (Comparative Example 2) 9 is a cross-sectional view of an optical element of Comparative Example 2. The optical element 1002 of Comparative Example 2 has a θ 1-1 = 70°, θ 1-2 = 4°, θ 2-1 = 70°, θ 2-2 =4°. The axial arrangement of each component was the same as in Comparative Example 1. As shown in FIG. 9, the first anisotropic molecules were hybrid-oriented so that the tilt angle continuously decreased from the first polarizer 10 side of the first retardation layer 20 toward the second retardation layer 30 side. The second anisotropic molecules were hybrid-oriented so that the tilt angle continuously decreased from the second polarizer 40 side of the second retardation layer 30 toward the first retardation layer 20 side. The thickness of the first retardation layer 20 and the thickness of the second retardation layer 30 were the same. In addition, the orientation direction of the first anisotropic molecules 21 was an azimuth angle of 180°, and the orientation direction of the second anisotropic molecules 31 was an azimuth angle of 0°.

[0129] The tilt angles of the first anisotropic molecules 21 and the second anisotropic molecules 31 were continuously changed between the first retardation layer 20 and the second retardation layer 30 so as to be symmetrical with respect to the interface between the first retardation layer 20 and the second retardation layer 30. The direction of change in the tilt angle of the first anisotropic molecules 21 and the direction of change in the tilt angle of the second anisotropic molecules 31 (white arrows in each retardation layer in FIG. 9) were set to be the same.

[0130] (Comparative Example 3) 10 is a cross-sectional view of an optical element of Comparative Example 3. The optical element 1003 of Comparative Example 3 has a θ 1-1 = 4°, θ 1-2 = 70°, θ 2-1 = 4°, θ 2-2= 70°. The axial arrangement of each component was the same as in Comparative Example 1. As shown in FIG. 10, 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 second retardation layer 30 side. 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 first retardation layer 20 side. The thickness of the first retardation layer 20 and the thickness of the second retardation layer 30 were the same. Furthermore, the orientation direction of the first anisotropic molecules 21 was an azimuth angle of 0°, and the orientation direction of the second anisotropic molecules 31 was an azimuth angle of 180°. The thickness of the first retardation layer 20 and the thickness of the second retardation layer 30 were the same.

[0131] The tilt angles of the first anisotropic molecules 21 and the second anisotropic molecules 31 were continuously changed between the first retardation layer 20 and the second retardation layer 30 so as to be symmetrical with respect to the interface between the first retardation layer 20 and the second retardation layer 30. The direction of change in the tilt angle of the first anisotropic molecules 21 and the direction of change in the tilt angle of the second anisotropic molecules 31 (white arrows in each retardation layer in FIG. 10 ) were set to be the same.

[0132] Comparative Example 4 Fig. 11 is a cross-sectional schematic diagram of the optical element of Comparative Example 4. As shown in Fig. 11, the optical element 1004 of Comparative Example 4 has the same configuration as Comparative Example 3, except that it has a negative C plate between the first retardation layer 20 and the second retardation layer 30. The negative C plate used had Rth = 300 nm.

[0133] The structures of Comparative Examples 1 to 4 are summarized in Table 1 below. In all of Comparative Examples 1 to 4, the in-plane retardation of the first retardation layer 20 and the second retardation layer 30 was 213 nm. In the table, 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 an azimuth angle of 0°.

[0134] [Table 1]

[0135] FIG. 12 shows the results of a simulation of the transmittance, viewing angle, and coloring of the optical element of Comparative Example 1. In Comparative Example 1, the results of the transmittance and viewing angle in FIG. 12 show that oblique light in the up and down azimuth directions (azimuth angles of 90°-270°) could be blocked, but the light-blocking region was asymmetrical with respect to the up and down azimuth directions. Hereinafter, transmitted light in oblique directions (particularly polar angles of 60° to 80°) will also be referred to as "oblique light." Furthermore, from the results of the coloring in FIG. 12, bluish coloring was observed at oblique angles of approximately 110° and approximately 250° (polar angles of approximately 60° to 80°) indicated by (i) in the figure, and yellowish coloring was observed at oblique angles of approximately 70° and approximately 290° (polar angles of approximately 60° to 80°) indicated by (ii) in the figure.

[0136] Fig. 13 shows the results of simulations of the transmittance viewing angle and coloring of the optical element of Comparative Example 2. The results of the transmittance viewing angle in Fig. 13 show that Comparative Example 2 was able to narrow the transmitted light in oblique directions in the vertical azimuth more than Comparative Example 1, and was able to block light symmetrically in the vertical azimuth. Furthermore, the results of the coloring in Fig. 13 show that coloring was observed near the azimuth angle of 90° and the oblique angle of azimuth angle of 270° (polar angle of 60°) shown in (i) in the figure, but the yellowish tint was suppressed more than in Comparative Example 1, and the coloring was a single blue color.

[0137] Fig. 14 shows the simulation results of the transmittance viewing angle and coloring of the optical element of Comparative Example 3. In Comparative Example 3, the transmittance viewing angle results in Fig. 14 show that although the light blocking range was symmetrical, the transmittance was high in oblique directions at azimuth angles of 90°-270°, and it was not possible to sufficiently narrow oblique light. Furthermore, the coloring results in Fig. 14 show that monochrome yellow coloring was observed in oblique directions at azimuth angles of 90° and 270°, as indicated by (i) in the figure.

[0138] Fig. 15 shows the results of simulation of the transmittance viewing angle and coloring of the optical element of Comparative Example 4. The results of the transmittance viewing angle in Fig. 15 show that Comparative Example 4 had a wider light-blocking region than Comparative Example 3, and was able to block light symmetrically with respect to azimuth angles of 90°-270°. The results of the coloring in Fig. 15 show that in the oblique directions at azimuth angles of 90° and 270°, as indicated by (i) in the figure, coloring that was more yellowish than Comparative Example 3 was observed.

[0139] From the results of the above comparative examples, although the light blocking effect of Comparative Example 3 was insufficient, since it was a single yellow color, it is expected that the coloring will be eliminated by combining it with Comparative Example 2, which is a single blue color. Furthermore, it is expected that the coloring will be further eliminated by combining Comparative Example 4, which is more yellow than Comparative Example 3, with Comparative Example 2. Below, a simulation was performed on an example in which the retardation layer had four layers.

[0140] Example 1 Example 1 is a specific example of Embodiment 1. The optical element of Example 1 is obtained by laminating the first and second retardation layers of the optical element of Comparative Example 3 and the first and second retardation layers of the optical element of Comparative Example 2, with the first retardation layer of the optical element of Comparative Example 3 facing the observation surface side. The first retardation layer 20 and the second retardation layer 30 of Example 1 have the same configuration as the first retardation layer 20 and the second retardation layer 30 of Comparative Example 3, and the third retardation layer 50 and the fourth retardation layer 60 of Example 1 have the same configuration as the first retardation layer 20 and the second retardation layer 30 of Comparative Example 2.

[0141] Fig. 2A is also a cross-sectional schematic diagram of the optical element of Example 1. As shown in Fig. 2A, the optical element 100 of Example 1 had a configuration including, in this order from the observation side, a first polarizer 10, a first retardation layer 20, a second retardation layer 30, a second polarizer 40, a third retardation layer 50, a fourth retardation layer 60, and a third polarizer 70. Single-layer absorption-type linear polarizers were used as the first polarizer, the second polarizer, and the third polarizer.

[0142] Fig. 3 is also a diagram showing the axial orientation of each member of the optical element of Example 1. As shown in Fig. 3, in Example 1, in a plan view, 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 are parallel to each other and are arranged parallel to an azimuth angle of 90 ° - 270 °. The slow axis (first slow axis) of the first retardation layer, the slow axis (second slow axis) of the second retardation layer, the slow axis (third slow axis) of the third retardation layer, and the slow axis (fourth slow axis) of the fourth retardation layer are parallel to each other and are arranged parallel to an azimuth angle of 0 ° - 180 °.

[0143] Example 2 Example 2 is a specific example of Embodiment 2. The optical element of Example 2 is a combination of the first and second retardation layers of the optical element of Comparative Example 4 and the first and second retardation layers of the optical element of Comparative Example 2, with the first retardation layer of the optical element of Comparative Example 4 facing the observation surface side. The first retardation layer 20 and the second retardation layer 30 of Example 2 had the same configuration as the first retardation layer 20 and the second retardation layer 30 of Comparative Example 4, and the third retardation layer 50 and the fourth retardation layer 60 of Example 1 had the same configuration as the first retardation layer 20 and the second retardation layer 30 of Comparative Example 2.

[0144] 4 is also a cross-sectional schematic diagram of the optical element of Example 2. The optical element 100B of Example 2 has the same configuration as Example 1, except that it has a negative C plate between the first retardation layer 20 and the second retardation layer 30. The negative C plate used had Rth=300 nm.

[0145] The structures of Examples 1 and 2 are summarized in Table 2 below. In Examples 1 and 2, 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 213 nm. In the table, the axial arrangement of the retardation layers 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 an azimuth angle of 0°.

[0146] [Table 2]

[0147] Fig. 16 shows the results of a simulation of the transmittance viewing angle and coloring of the optical element of Example 1. From the results of the transmittance viewing angle in Fig. 16, Example 1 was able to narrow down oblique light in the up and down azimuths (azimuth angles of 90°-270°) more than Comparative Example 1, and was able to block light symmetrically with respect to the azimuth angles of 90°-270°. Furthermore, from the results of the coloring in Fig. 16, it was possible to improve the overall coloring by combining Comparative Example 2, in which a single blue coloring was observed, with Comparative Example 3, in which a single yellowish coloring was observed, in the oblique directions at azimuth angles of 90° and 270°, as shown by (i) in the figure.

[0148] Fig. 17 shows the results of simulations of the transmittance viewing angle and coloring of the optical element of Example 2. In Example 2, the results of the transmittance viewing angle in Fig. 17 show that light could be blocked symmetrically with respect to an azimuth angle of 90°-270°, and that oblique light in the up and down azimuths (azimuth angles of 90°-270°) could be further narrowed than in Example 1. Furthermore, the results of the coloring in Fig. 17 show that in the oblique directions of azimuth angles of 90° and 270° shown in (i) in the figure, the light blocking effect was stronger than in Example 1, and the coloring was also darker, thereby significantly improving the blue coloring seen in Example 1 and resulting in an appearance close to achromatic (black), and further reducing the coloring of oblique light.

[0149] Fig. 18 is a graph in which the transmittances of Comparative Example 2, Example 1, and Example 2 are superimposed. Fig. 18 is a graph showing the transmittances of Comparative Example 2, Example 1, and Example 2 when the polar angle is changed from 0° to 80° in the up and down azimuth (azimuth angles of 90°-270°), with the transmittance in the normal direction being 100%. The transmittances at an azimuth angle of 90° and a polar angle of 60° at an azimuth angle of 270° in Fig. 18 are summarized in Table 3 below.

[0150] [Table 3]

[0151] 18 and Table 3, Comparative Example 2 had a transmittance of 17.2% at a polar angle of 60° at an azimuth angle of 90° and at a polar angle of 60° at an azimuth angle of 270°, whereas Example 1 had a transmittance of 10.2% at the polar angle of 60°, improving the shading effect (louver performance). Furthermore, Example 2, in which a negative C plate was added, had a transmittance of 1% at the polar angle of 60°, further improving louver performance compared to Example 1.

[0152] Table 4 below summarizes the chromaticity shifts of Comparative Example 2, Example 1, and Example 2. The chromaticity shift Δxy is expressed by the following formula. In the formula below, x0 and y0 are the x and xy values, respectively, on the xy chromaticity diagram in the normal direction of the optical element. Calculations were performed using the x and y values ​​on the xy chromaticity diagram for Comparative Example 2, 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. The smaller the Δxy value, the closer the appearance is to achromatic color (black), indicating an improvement in color.

[0153]

number

[0154] [Table 4]

[0155] As shown in Table 4, it was confirmed that Examples 1 and 2 had less chromaticity shift and improved color tone compared to Comparative Example 2. Furthermore, Example 2 was able to improve color tone more than Example 1.

[0156] (Comparative Example 5) The transmittance and coloring of the optical element according to Comparative Example 5 were investigated as a polarizing plate louver having a single retardation layer corresponding to the prior art. FIG. 19 is a cross-sectional schematic diagram of the optical element according to Comparative Example 5. As shown in FIG. 19, the optical element according to Comparative Example 5 was configured to include a first polarizer 1010, a first retardation layer 1020, and a second polarizer 1040, in this order. The first polarizer 1010 and the second polarizer 1040 were the same as those used in Comparative Example 1. The anisotropic molecules 1021 contained in the first retardation layer 1020 were not hybrid-oriented, and the tilt angles of the anisotropic molecules 1021 located on the first polarizer 1010 side and the anisotropic molecules 1021 located on the second polarizer 1040 side were both set to 50°.

[0157] Fig. 20 is a diagram showing the axial orientations of the components of the optical element of Comparative Example 5. As shown in Fig. 20, in a plan view, the absorption axis (first absorption axis) of the first polarizer and the absorption axis (second absorption axis) of the second polarizer were arranged parallel to each other at an azimuth angle of 90°-270°. The slow axis of the first retardation layer 1020 was perpendicular to the first absorption axis. The orientation orientation of the anisotropic molecules contained in the first retardation layer 1020 was set to an azimuth angle of 180°.

[0158] FIG. 21 shows the results of simulations of the transmittance, viewing angle, and coloring of the optical element of Comparative Example 5. From the results of transmittance and viewing angle in FIG. 21, it can be seen that in Comparative Example 5, although the light-shielding region was symmetric (bilaterally symmetric) with respect to the azimuth angles of 90°-270°, the transmission region was wide, and the light-shielding effect in the oblique directions of the vertical azimuth was insufficient. As shown in the contour diagram showing the coloring, yellow ((i) in the contour diagram) and blue-purple ((ii) in the contour diagram) coloring was intense in the oblique directions (polar angles of 40° or more), which was thought to affect the viewing angle performance of the display. Compared to Comparative Example 5, Examples 1 and 2 provided sufficient light-shielding in the vertical azimuth, the light-shielding region was bilaterally symmetric, and coloring was sufficiently suppressed.

[0159] Examples 3 to 5 Except for changing the retardation of the negative C plate to 100 nm, 200 nm, and 400 nm, the optical elements of Examples 3 to 5 were produced in the same manner as in Example 2. Table 5 below summarizes the transmittance at an azimuth angle of 90° and a polar angle of 60°.

[0160] [Table 5]

[0161] As shown in Table 5, it was confirmed that when the phase difference of the negative C plate is 300 nm or more, the transmittance in the oblique direction can be reduced to approximately 1%.

[0162] FIG. 19 is a graph showing the relationship between thickness direction retardation and transmittance of a negative C plate. FIG. 20 is a graph showing the relationship between thickness direction retardation and Δxy of a negative C plate. Ideally, a polarizing louver has a transmittance of 2% or less at an azimuth angle of 90° and a polar angle of 60°, and a chromaticity shift Δxy of 0.2 or less at an azimuth angle of 90° and a polar angle of 60°. As shown in FIG. 19, when the thickness direction retardation of the negative C plate is approximately 250 nm or more, the transmittance at an azimuth angle of 90° and a polar angle of 60° is 2% or less. As shown in FIG. 20, when the thickness direction retardation of the negative C plate is approximately 320 nm or less, the chromaticity shift Δxy is 0.2 or less. From these results, it is preferable that the thickness direction retardation of the negative C plate is 250 nm or more and 320 nm or less. [Explanation of symbols]

[0163] 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, 100A, 100B, 1001, 1002, 1003, 1004: 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 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; 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, 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, a slow axis of the third retardation layer and a slow axis of the fourth retardation layer are parallel to each other, 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, the first anisotropic molecules change so that a tilt angle increases from the first polarizer side of the first retardation layer toward the second retardation layer side, the second anisotropic molecules change so that a tilt angle increases from the second polarizer side of the second retardation layer toward the first retardation layer side, 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, An optical element, wherein the fourth anisotropic molecules change so that a tilt angle thereof becomes smaller from the third polarizer side toward the third retardation layer side of the fourth retardation layer.

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, 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, 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°; The optical element according to claim 1 , wherein, in a plan view, the alignment direction of the third anisotropic molecules and the alignment direction of the fourth anisotropic molecules differ by 180°±3°.

3. 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 direction of each of the first anisotropic molecules and the fourth anisotropic molecules is 0°±3°, and the orientation direction of each of the second anisotropic molecules and the third anisotropic molecules is 180°±3°, or The optical element of claim 2, wherein the orientation direction of each of the first anisotropic molecules and the fourth anisotropic molecules is 180°±3°, and the orientation direction of each of the second anisotropic molecules and the third anisotropic molecules is 0°±3°.

4. The optical element according to claim 1 , further comprising a negative C plate between the first retardation layer and the second retardation layer.

5. 5. The optical element according to claim 4, wherein the retardation in the thickness direction of the negative C plate is 250 nm or more and 320 nm or less.

6. The optical element according to claim 1 , wherein, in a plan view, the slow axis of the third retardation layer and the slow axis of the fourth retardation layer are parallel to the slow axis of the first retardation layer.

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

8. 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.

9. 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.

10. A liquid crystal panel, an optical element according to any one of claims 1 to 9, 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.

11. 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 10 , 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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