Optical laminate and image display device

Abstract

The invention provides an optical laminate capable of suppressing light leakage in an inclined direction and an image display device. An optical laminate according to an embodiment of the present invention is provided with a polarizer including a polarizer, a first phase difference layer, a second phase difference layer, and a third phase difference layer in this order. The refractive index characteristic of at least one of the second phase difference layer and the third phase difference layer shows nzgt; nxgt; n < y >.

Description

Technical Field The present invention relates to an optical laminate and an image display device. Background Art In an image display device such as an organic electroluminescence (EL) display device, various optical laminates (for example, Patent Document 1) in which a polarizing plate and an optical compensation film are combined are used in order to achieve optical characteristics suitable for the use. For example, an optical laminate has been proposed in which a retardation layer having a refractive index characteristic showing a relationship of nx > ny = nz, a retardation layer having a refractive index characteristic showing a relationship of nz > nx = ny, and a retardation layer having a refractive index characteristic showing a relationship of nx > ny ≥ nz are sequentially laminated on a polarizing plate including a polarizer. Prior Art Documents Patent Documents Patent Document 1: Japanese Patent Application Laid-Open No. 2018-180224 Summary of the Invention Problems to be Solved by the Invention However, in an image display device using the above-described optical laminate, there is a tendency for light leakage to occur in an inclined direction. An object of the present invention is to provide an optical laminate for an image display device capable of suppressing light leakage in an inclined direction. Means for Solving the Problems

[0001] The optical laminate according to an embodiment of the present invention sequentially includes a polarizing plate including a polarizer, a first retardation layer, a second retardation layer, and a third retardation layer. The refractive index characteristic of at least one of the second retardation layer and the third retardation layer shows a relationship of nz > nx > ny.

[0002] In the optical laminate according to [1] above, the refractive index characteristic of the first retardation layer may show a relationship of nx > ny = nz.

[0003] In the optical laminate according to [1] or [2] above, the refractive index characteristic of any one of the second retardation layer and the third retardation layer may show a relationship of nx > ny = nz.

[0004] In the optical laminate according to any one of [1] to [3] above, the refractive index characteristics of the second retardation layer may exhibit the relationship nz > nx > ny. Alternatively, the in-plane retardation Re(550) of the first retardation layer may be 130 nm or more and 150 nm or less, the in-plane retardation Re(550) of the second retardation layer may be 140 nm or more and 160 nm or less, and the in-plane retardation Re(550) of the third retardation layer may be 190 nm or more and 210 nm or less. Alternatively, the angle formed by the absorption axis of the polarizer and the slow axis of the first retardation layer may be 13.5° or more and 33.5° or less, the angle formed by the absorption axis of the polarizer and the slow axis of the second retardation layer may be -10° or more and 10° or less, and the angle formed by the absorption axis of the polarizer and the slow axis of the third retardation layer may be 62.5° or more and 82.5° or less.

[0005] In the optical laminate according to any one of [1] to [3] above, the refractive index characteristics of the third retardation layer may exhibit the relationship nz > nx > ny. Alternatively, the in-plane retardation Re(550) of the first retardation layer may be 185 nm or more and 205 nm or less, the in-plane retardation Re(550) of the second retardation layer may be 110 nm or more and 130 nm or less, and the in-plane retardation Re(550) of the third retardation layer may be 50 nm or more and 70 nm or less. Alternatively, the angle formed by the absorption axis of the polarizer and the slow axis of the first retardation layer may be 0° or more and 20° or less, the angle formed by the absorption axis of the polarizer and the slow axis of the second retardation layer may be 30° or more and 50° or less, and the angle formed by the absorption axis of the polarizer and the slow axis of the third retardation layer may be 80° or more and 100° or less.

[0006] In the optical laminate according to any one of [1] to [5] above, the retardation layer whose refractive index characteristics exhibit the relationship nz > nx > ny may be composed of a resin film.

[0007] An image display device according to another aspect of the present invention includes an image display panel and the optical laminate according to any one of [1] to [6] above. Advantages of the Invention According to an embodiment of the present invention, an optical laminate capable of providing an image display device with suppressed light leakage in the tilt direction can be provided. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a cross-sectional schematic view of an optical laminate according to an embodiment of the present invention. Figure 2A It is an equal-contrast curve distribution diagram from the perspective of Example 1. Figure 2BIt is an equal contrast curve distribution diagram from the perspective of Example 2. Figure 2C It is an equal contrast curve distribution diagram from the perspective of Example 3. Figure 3A It is an equal contrast curve distribution diagram from the perspective of Comparative Example 1. Figure 3B It is an equal contrast curve distribution diagram from the perspective of Comparative Example 2. Explanation of reference numerals 10 First retardation layer 20 Second retardation layer 30 Third retardation layer 40 Polarizer 41 Polarizer 100 Optical laminate Detailed implementation manners Hereinafter, representative embodiments of the present invention will be described, but the present invention is not limited to these embodiments. It should be noted that in this specification, the expression "A and / or B" means any one of "A and B", "A", or "B". (Definition of terms and symbols) The definitions of the terms and symbols in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the in-plane refractive index is the largest (i.e., the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane retardation (Re) "Re(λ)" is the in-plane retardation measured with light of wavelength λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light of wavelength 550 nm at 23°C. When the thickness of the layer (thin film) is set to d (nm), Re(λ) is obtained by the formula: Re(λ) = (nx - ny) × d. It should be noted that in this specification, sometimes the "in-plane retardation Re(λ) of the first retardation layer" is referred to as "Re 1 (λ)", the "in-plane retardation Re(λ) of the second retardation layer" is referred to as "Re 2 (λ)", and the "in-plane retardation Re(λ) of the third retardation layer" is referred to as "Re 3 (λ)". (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light of wavelength 550 nm at 23°C. When the thickness of the layer (thin film) is set to d (nm), Rth(λ) is obtained by the formula: Rth(λ) = (nx - nz) × d. In addition, in this specification, the "retardation Rth(λ) in the thickness direction of the first retardation layer" is sometimes referred to as "Rth 1 (λ)", the "in-plane retardation Re(λ) of the second optical retardation layer" is referred to as "Rth 2 (λ)", and the "in-plane retardation Re(λ) of the third retardation layer" is referred to as "Rth 3 (λ)". (4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re. (5) Substantially parallel or orthogonal Expressions such as "substantially orthogonal" and "substantially perpendicular" include cases where the angle formed by the two directions is 90° ± 3°, and expressions such as "substantially parallel" and "substantially parallel" include cases where the angle formed by the two directions is 0° ± 3°. In addition, "crossing without being substantially orthogonal" means that the angle formed by the two directions is not substantially orthogonal and not substantially parallel. More specifically, the expression "crossing without being substantially orthogonal" includes cases where the angle formed by the two directions exceeds 3° and is less than 87°, and cases where it exceeds 93° and is less than 177°, preferably 5° or more and 85° or less, or 95° or more and 175° or less. (6) Angle When an angle is mentioned in this specification, the angle includes both clockwise and counterclockwise with respect to the reference direction. Therefore, for example, "45°" means ±45°. (7) Name of the retardation film In this specification, a layer (thin film) showing a refractive index characteristic of nz > nx > ny is sometimes referred to as a "positive B plate", a layer (thin film) showing a refractive index characteristic of nx > ny = nz is referred to as a "positive A plate", a layer (thin film) showing a refractive index characteristic of nz > nx = ny is referred to as a "positive C plate", and a layer (thin film) showing a refractive index characteristic of nx > ny > nz is referred to as a "negative B plate". It should be noted that the above "nx = ny" includes not only the case where nx and ny are exactly the same, but also the case where nx and ny are substantially the same. The same applies to "ny = nz". A. Overall structure of the optical laminate Figure 1It is a cross-sectional schematic view of an optical laminate according to an embodiment of the present invention. The illustrated optical laminate 100 includes a polarizer 40 including a polarizer 41, a first retardation layer 10, a second retardation layer 20, and a third retardation layer 30 in this order from the upper side of the drawing. The upper side of the drawing is the visually recognizable side, and the lower side of the drawing is the image display panel side. The polarizer 40 includes a polarizer 41 and a protective layer 42 disposed on one side of the polarizer 41 (the visually recognizable side in the illustrated example). The illustrated polarizer 40 is a so-called single-sided protected polarizer. Depending on the purpose, other protective layers (inner protective layers: not shown) may be disposed on the side of the polarizer 41 opposite to the protective layer 42. That is, the polarizer may be a double-sided protected polarizer. From the viewpoint of thinning the optical laminate, the inner protective layer can be omitted. In the illustrated example, the first retardation layer 10 is disposed adjacent to the polarizer 40. More specifically, the first retardation layer 10 is disposed adjacent to the polarizer 41. In this specification, "disposed adjacent to" means directly laminated or laminated only with an adhesive layer (for example, an adhesive layer or an adhesive layer). That is, it means that no other layer having an optical function (hereinafter sometimes referred to as an "optical function layer") is interposed between the polarizer 40 and the first retardation layer 10. In the illustrated example, the second retardation layer 20 is disposed on the side opposite to the polarizer 40 with respect to the first retardation layer 10 and adjacent to the first retardation layer 10. In the illustrated example, the third retardation layer 30 is disposed on the side opposite to the first retardation layer 10 with respect to the second retardation layer 20 and adjacent to the second retardation layer 20. In an embodiment of the present invention, the refractive index characteristics of at least one of the second retardation layer 20 and the third retardation layer 30 exhibit a relationship of nz > nx > ny. According to such a configuration, when the optical laminate is applied to an image display device, it is possible to suppress the deviation of the brightness in the tilt direction in pure black display. As a result, in the image display device, the optical laminate can maintain a low brightness in the front direction in pure black display and suppress light leakage in the tilt direction. In conventional optical laminates, when observed from a specific azimuth angle in the oblique direction, there is an azimuth angle range in which the brightness in pure black display relatively increases, resulting in a deviation in brightness. As a result, when a conventional optical laminate is applied to an image display device, there is a tendency for light leakage to occur. In contrast, in the optical laminate according to an embodiment of the present invention, it is possible to suppress the occurrence of deviation in brightness in the oblique direction in pure black display. Therefore, it is considered that if this optical laminate is applied to an image display device, light leakage in the oblique direction can be suppressed. The reason is not necessarily clear, but it is presumed to be the following mechanism. Generally, in an optical laminate having a plurality of retardation layers, the refractive index anisotropy of the laminate when adding each retardation layer becomes a refractive index ellipsoid. In this ellipsoid, when the azimuth angle is changed, the cross-sectional shape may vary depending on the angle. As a result, depending on the angle at which this ellipsoid is observed, a difference in brightness (i.e., a deviation in brightness) may occur. In contrast, in the optical laminate according to an embodiment of the present invention, the shape of the cross-section of the ellipsoid obtained based on the addition of the retardation layers becomes a shape close to a perfect circle. Thus, even when the azimuth angle is changed (even when the observation angle is changed), the difference in the cross-sectional shape due to the angle becomes smaller. As a result, it is presumed that the difference in brightness at each azimuth angle becomes smaller and the deviation in brightness becomes smaller. It should be noted that the above is only a presumed mechanism and does not limit the present invention. Therefore, with the optical laminate according to an embodiment of the present invention, an image display device with excellent viewing angle dependence can be realized. It should be noted that the brightness in the oblique direction in pure black display can be obtained, for example, by measuring the brightness while changing the azimuth angle in 5° increments at a polar angle of 60°. The method and conditions for measuring "brightness" will be described in detail in the following example section. As described above, the refractive index characteristics of at least one of the second retardation layer 20 and the third retardation layer 30 can exhibit the relationship of nz > nx > ny. Preferably, the refractive index characteristics of either the second retardation layer 20 or the third retardation layer 30 exhibit the relationship of nz > nx > ny. The first retardation layer 10 preferably has refractive index characteristics exhibiting the relationship of nx > ny = nz. In this case, preferably, the refractive index characteristics of one of the second retardation layer 20 and the third retardation layer exhibit the relationship of nz > nx > ny, and the refractive index characteristics of the other exhibit the relationship of nx > ny = nz. In other words, when the first retardation layer 10 is a positive A plate, preferably, one of the second retardation layer 20 and the third retardation layer 30 is a positive B plate and the other is a positive A plate. When the refractive index characteristics of the third retardation layer 30 exhibit the relationship nz > nx > ny, it is preferable that the refractive index characteristics of the first retardation layer 10 and the second retardation layer 20 both exhibit the relationship nx > ny = nz. In other words, when the third retardation layer 30 is a positive B plate, it is preferable that the first retardation layer 10 and the second retardation layer 20 are positive A plates. In this case, it is possible to more favorably suppress the deviation of the brightness in the tilt direction in the black display of the optical laminate. Furthermore, it is less likely to affect the hue change in the front direction in the black display of the optical laminate, and it is also possible to suppress the deviation of the hue change in the tilt direction in the black display. When the refractive index characteristics of the second retardation layer 20 exhibit the relationship nz > nx > ny, it is preferable that the refractive index characteristics of the first retardation layer 10 and the third retardation layer 30 both exhibit the relationship nx > ny = nz. That is, when the second retardation layer 20 is a positive B plate, it is preferable that the first retardation layer 10 and the third retardation layer 30 are positive A plates. In this case, it is possible to more favorably suppress the deviation of the brightness in the tilt direction in the black display of the optical laminate. Furthermore, it is even less likely to affect the hue change in the front direction in the black display of the optical laminate, and it is also possible to more favorably suppress the deviation of the hue change in the tilt direction in the black display. It is speculated that the reason for suppressing not only the deviation of the brightness in the tilt direction in the black display but also the deviation of the hue change in the tilt direction in the black display is that if such a configuration is adopted, the cross-sectional shape of the refractive index ellipsoid when adding the refractive indices of the retardation layers is closer to a perfect circle when observed from each azimuth angle direction. The optical laminate 100 can be in a single sheet form or in a long strip form. In this specification, "long strip form" means an elongated shape that is sufficiently long relative to the width, for example, including an elongated shape where the length is 10 times or more, preferably 20 times or more, relative to the width. The long strip-shaped optical laminate can be wound into a roll. Practically, an adhesive layer (not shown) is provided on the side of the third retardation layer 30 opposite to the polarizing plate 40, and the optical laminate 100 can be attached to an image display. It is preferable to temporarily stick a release liner on the surface of the adhesive layer until the optical laminate 100 is put into use. By temporarily sticking the release liner, a roll can be formed while protecting the adhesive layer. Hereinafter, specific combinations of the first retardation layer, the second retardation layer, and the third retardation layer in the optical laminate will be described. By combining the in-plane retardation Re(λ) of each retardation layer, the angle formed by the slow axis of each retardation layer and the absorption axis of the polarizer, and the Nz coefficient of the retardation layer exhibiting the refractive index characteristics of nz > nx > ny so as to be within a specific range, the optical laminate according to the embodiment of the present invention can exhibit a more remarkable effect. A-1. First optical laminate In one embodiment, the refractive index characteristics of the first retardation layer exhibit a relationship of nx > ny = nz, the refractive index characteristics of the second retardation layer exhibit a relationship of nz > nx > ny, and the refractive index characteristics of the third retardation layer exhibit a relationship of nx > ny = nz. That is, the first retardation layer is a positive A plate, the second retardation layer is a positive B plate, and the third retardation layer is a positive A plate. Sometimes such an optical laminate is referred to as a "first optical laminate". According to the first optical laminate, when the optical laminate is applied to an image display device, it is possible to more favorably suppress the deviation of the brightness in the tilt direction in pure black display. As a result, when the first optical laminate is applied to an image display device, it is possible to further suppress the light leakage in the tilt direction. In the first optical laminate, the in-plane retardation Re 1 (550) of the first retardation layer is preferably 130 nm or more, more preferably 132 nm or more, still more preferably 135 nm or more, and particularly preferably 140 nm or more. The in-plane retardation Re 1 (550) of the first retardation layer is preferably 150 nm or less, more preferably 148 nm or less, still more preferably 146 nm or less, and particularly preferably 145 nm or less. In the first optical laminate, the angle formed by the absorption axis of the polarizer and the slow axis of the first retardation layer is preferably 13.5° or more and 33.5° or less, more preferably 15° or more and 30° or less, still more preferably 18.5° or more and 28.5° or less, and particularly preferably 20° or more and 27° or less. It should be noted that the "angle formed by the absorption axis of the polarizer and the slow axis of the first retardation layer" is sometimes referred to as the "slow axis angle of the first retardation layer". The same applies to the second retardation layer and the third retardation layer. In the first optical laminate, if Re 1 (550) and / or the slow axis angle of the first retardation layer is within the above range, the deviation of the brightness in the tilt direction in pure black display can be further suppressed. As a result, when the first optical laminate is applied to an image display device, the light leakage in the tilt direction can be further suppressed. That is, the effects brought about by the embodiments of the present invention can be significantly exerted. In the first optical laminate, the in-plane retardation Re 2 (550) of the second retardation layer is preferably 140 nm or more, more preferably 142 nm or more, still more preferably 145 nm or more. The in-plane retardation Re 2 (550) of the second retardation layer is preferably 160 nm or less, more preferably 158 nm or less, still more preferably 155 nm or less. In the first optical laminate, the Nz coefficient of the second retardation layer is less than 0, preferably more than -0.3 and less than 0, more preferably -0.25 or more and -0.05 or less. If the Nz coefficient of the second retardation layer is within the above range, the cross-sectional shape of the refractive index ellipsoid when adding the refractive indices of the respective retardation layers in the first optical laminate is observed from each azimuth angle direction becomes a shape closer to a perfect circle. As a result, in the first optical laminate, it is possible to particularly suppress the deviation of the brightness in the tilt direction in pure black display. In the first optical laminate, the slow axis angle of the second retardation layer is preferably -10° or more and 10° or less, more preferably -8° or more and 8° or less, further preferably -5° or more and 5° or less, and particularly preferably -3° or more and 3° or less. The slow axis angle of the second retardation layer can be, for example, 0°. In the first optical laminate, if Re 2 (550) and / or the slow axis angle of the second retardation layer is within the above range, the effects brought about by the embodiments of the present invention can be more significantly exhibited. In the first optical laminate, the in-plane retardation Re 3 (550) of the third retardation layer is preferably 190 nm or more, more preferably 195 nm or more, and further preferably 198 nm or more. The in-plane retardation Re 3 (550) of the third retardation layer is preferably 210 nm or less, more preferably 208 nm or less, and further preferably 206 nm or less. In the first optical laminate, the slow axis angle of the third retardation layer is preferably 62.5° or more and 82.5° or less, more preferably 65° or more and 80° or less, and further preferably 67.5° or more and 77.5° or less. In the first optical laminate, if Re 3 (550) and / or the slow axis angle of the third retardation layer is within the above range, the effects brought about by the embodiments of the present invention can be more significantly exhibited. A-2. Second optical laminate In one embodiment, the refractive index characteristics of the first retardation layer show a relationship of nx > ny = nz, the refractive index characteristics of the second retardation layer show a relationship of nx > ny = nz, and the refractive index characteristics of the third retardation layer show a relationship of nz > nx > ny. That is, the first retardation layer is a positive A plate, the second retardation layer is a positive A plate, and the third retardation layer is a positive B plate. Sometimes, an optical laminate including such a combination of the first retardation layer, the second retardation layer, and the third retardation layer is referred to as a "second optical laminate". According to the second optical laminate, it is possible to further suppress the deviation of the brightness in the tilt direction in the pure black display of the optical laminate. As a result, when the second optical laminate is applied to an image display device, it is possible to further suppress the light leakage in the tilt direction. In the second optical laminate, the in-plane retardation Re 1 (550) is preferably 185 nm or more, more preferably 187 nm or more, further preferably 190 nm or more, and particularly preferably 193 nm or more. The in-plane retardation Re 1 (550) is preferably 205 nm or less, more preferably 203 nm or less, and further preferably 200 nm or less. In the second optical laminate, the slow axis angle of the first retardation layer is preferably 0° or more and 20° or less, more preferably 3° or more and 17° or less, further preferably 5° or more and 15° or less, and particularly preferably 8° or more and 13° or less. In the second optical laminate, if Re 1 (550) and / or the slow axis angle of the first retardation layer is within the above range, the effects brought by the embodiments of the present invention can be significantly exerted. In the second optical laminate, the in-plane retardation Re of the second retardation layer 2 (550) is preferably 110 nm or more, more preferably 112 nm or more, and further preferably 115 nm or more. The in-plane retardation Re of the second retardation layer 2 (550) is preferably 130 nm or less, more preferably 128 nm or less, and further preferably 125 nm or less. In the second optical laminate, the slow axis angle of the second retardation layer is preferably 30° or more and 50° or less, more preferably 35° or more and 45° or less, and further preferably 37.5° or more and 47.5° or less. In the second optical laminate, if Re 2 (550) and / or the slow axis angle of the second retardation layer is within the above range, the effects brought by the embodiments of the present invention can be significantly exerted. In the second optical laminate, the in-plane retardation Re of the third retardation layer 3(550) is preferably 50 nm or more, more preferably 55 nm or more, and further preferably 58 nm or more. The in-plane retardation Re of the third retardation layer 3 (550) is preferably 70 nm or less, more preferably 65 nm or less, and further preferably 63 nm or less. In the second optical laminate, the Nz coefficient of the third retardation layer is preferably more than -0.3 and less than 0. The Nz coefficient of the third retardation layer is more preferably -0.25 or more and -0.05 or less. In the second optical laminate, the slow axis angle of the third retardation layer is preferably 80° or more and 100° or less, more preferably 85° or more and 95° or less, and further preferably 87.5° or more and 92.5° or less. The slow axis angle of the third retardation layer can be, for example, 90°. In the second optical laminate, if Re 3 (550) and / or the slow axis angle of the third retardation layer is within the above range, the second optical laminate can exhibit a more remarkable effect. As a representative example, the case where the first retardation layer is a positive A plate and one of the second retardation layer and the third retardation layer is a positive B plate has been described, but the configuration of the optical laminate of the embodiment of the present invention is not limited to these. For example, the first retardation layer can be a positive A plate, and both the second retardation layer and the third retardation layer can be positive B plates. Further, within the scope not departing from the purpose of the embodiment of the present invention, the first retardation layer and the layer that is not a positive B plate among the second retardation layer and the third retardation layer can have any appropriate refractive index characteristics and slow axis angles corresponding to the target. In the optical laminate of the embodiment of the present invention, at least one of the second retardation layer and the third retardation layer is a positive B plate. For example, the first retardation layer can be a layer other than a positive A plate. In addition, the layer that is not a positive B plate among the second retardation layer and the third retardation layer can be a layer other than a positive A plate. As a layer other than a positive A plate, for example, a negative B plate can be cited. Hereinafter, each component constituting the optical laminate will be described. B. Polarizer B-1. Polarizer As the polarizer, any appropriate polarizer can be used. For example, the resin film forming the polarizer can be a single-layer resin film or a laminate of two or more layers. As a specific example of a polarizer composed of a single-layer resin film, there can be mentioned a polarizer obtained by subjecting a hydrophilic polymer film such as a polyvinyl alcohol (PVA) - based film, a partially formalized PVA - based film, an ethylene - vinyl acetate copolymer - based partially saponified film, etc. to a dyeing treatment and a stretching treatment using a dichroic substance such as iodine or a dichroic dye, a dehydrated product of PVA, a polyene - based oriented film such as a hydrochloric acid - removed product of polyvinyl chloride, etc. From the aspect of excellent optical properties, a polarizer obtained by dyeing a PVA - based film with iodine and performing uniaxial stretching is preferably used. The above - mentioned iodine - based dyeing is carried out, for example, by immersing the PVA - based film in an iodine aqueous solution. The stretching ratio of the above - mentioned uniaxial stretching is preferably 3 times or more and 7 times or less. The stretching can be carried out after the dyeing treatment, or can be carried out while dyeing. In addition, dyeing can also be carried out after stretching. As needed, a swelling treatment, a cross - linking treatment, a cleaning treatment, a drying treatment, etc. are carried out on the PVA - based film. For example, by immersing the PVA - based film in water before dyeing for water washing, not only can the dirt and anti - sticking agent on the surface of the PVA - based film be cleaned, but also the PVA - based film can be swollen to prevent uneven dyeing, etc. As a specific example of a polarizer obtained by using a laminate, a polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate can be cited. A polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate can be produced, for example, by the following method: coating a PVA-based resin solution on the resin substrate and drying it to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate to form a polarizer from the PVA-based resin layer. In an embodiment of the present invention, it is preferable to form a PVA-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further include air stretching the laminate at a high temperature (for example, 95 °C or higher) before stretching in the aqueous boric acid solution as needed. In addition, in an embodiment of the present invention, it is preferable to subject the laminate to a dry shrinkage treatment in which the laminate is heated while being conveyed in the length direction to shrink by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes sequentially performing an air-assisted stretching treatment, a dyeing treatment, a water stretching treatment, and a dry shrinkage treatment on the laminate. By introducing the assisted stretching, even when PVA is coated on a thermoplastic resin, the crystallinity of PVA can be improved, and high optical characteristics can be achieved. In addition, by simultaneously improving the orientation of PVA in advance, problems such as a decrease in the orientation of PVA and dissolution when immersed in water in subsequent dyeing and stretching processes can be prevented, and high optical characteristics can be achieved. Further, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain a halide, the disorder of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed. Thereby, the optical characteristics of the polarizer obtained through treatment processes such as dyeing treatment and water stretching treatment in which the laminate is immersed in a liquid can be improved. Further, by using the dry shrinkage treatment to shrink the laminate in the width direction, the optical characteristics can be improved. The obtained laminate of the resin substrate / polarizer can be used directly (that is, the resin substrate can be used as a protective layer of the polarizer), or the resin substrate can be peeled off from the laminate of the resin substrate / polarizer, and any appropriate protective layer according to the purpose can be laminated on the peeled surface for use. The details of such a method for manufacturing a polarizer are described, for example, in Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent No. 6470455. The entire descriptions of these publications are incorporated herein by reference in their entirety. The thickness of the polarizer can be, for example, 1 μm or more and 80 μm or less. The thickness of the polarizer is preferably 1 μm or more, more preferably 3 μm or more. The thickness of the polarizer is preferably 15 μm or less, more preferably 12 μm or less, and further preferably 8 μm or less. If the thickness of the polarizer is within such a range, curling during heating can be suppressed well, and good appearance durability during heating can be obtained. The polarizer preferably exhibits absorption dichroism at any wavelength in the wavelength range of 380 nm to 780 nm. The monomer transmittance of the polarizer is, for example, 41.5% or more and 46.0% or less, preferably 43.0% or more and 46.0% or less, more preferably 44.5% or more and 46.0% or less. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and further preferably 99.9% or more. B-2. Protective layer The protective layer is formed of any suitable thin film that can be used as a protective thin film for the polarizer. Specific examples of the material that is the main component of this thin film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, acetate-based, etc. transparent resins. In addition, thermosetting resins or ultraviolet curable resins such as (meth)acrylic-based, urethane-based, (meth)acrylic urethane-based, epoxy-based, silicone-based, etc. can also be cited. In addition to these, for example, vitreous polymers such as siloxane-based polymers can also be cited. In addition, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01 / 37007) can also be used. As the material of this thin film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used. Specific examples include a resin composition having an alternating copolymer formed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. This polymer film can be, for example, an extrusion molded product of the above resin composition. As described above, the optical laminate is typically disposed on the visual recognition side of the image display device, and the protective layer 42 is disposed on its visual recognition side. Therefore, surface treatments such as hard coat treatment, antireflection treatment, antiadhesion treatment, antiglare treatment, etc. can be performed on the protective layer as needed. Furthermore, a treatment for improving visual recognition when visually recognizing through polarized sunglasses (typically imparting an (elliptical) polarization function, imparting an ultra-high retardation) can be performed on the protective layer as needed. By performing such treatments, excellent visual recognition can be achieved even when visually recognizing the display screen through a polarized lens such as polarized sunglasses. Therefore, the optical laminate can also be suitably applied to an image display device that can be used outdoors. The inner protective layer (if present) is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) is from 0 nm to 10 nm and the retardation in the thickness direction Rth(550) is from -10 nm to +10 nm. The thickness of the protective layer is preferably 5 μm or more, more preferably 10 μm or more. The thickness of the protective layer is preferably 80 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. It should be noted that in the case where surface treatment is performed, the thickness of the protective layer is the thickness including the thickness of the surface treatment layer. The same applies to the thickness of the inner protective layer (if present). C. First retardation layer The light transmittance of the first retardation layer at a wavelength of 550 nm is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. The theoretical upper limit of the light transmittance is 100%, but due to surface reflection caused by the refractive index difference between air and the retardation film, the achievable upper limit of the light transmittance is approximately 94%. As described above, the refractive index characteristics of the first retardation layer preferably show the relationship of nx > ny = nz. That is, the first retardation layer is preferably a positive A plate. As the material for forming the first retardation layer, any suitable material can be used as long as the above-described characteristics can be obtained. Specifically, the first retardation layer can be an orientation cured layer of a liquid crystal compound (liquid crystal orientation cured layer), or a retardation film (stretched film of a polymer film). In the case where the first retardation layer is a liquid crystal orientation cured layer, by using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be significantly increased compared with non-liquid crystal materials, and thus the thickness of the retardation layer for obtaining the desired in-plane retardation can be significantly reduced. As a result, further thinning of the polarizing plate (and as a result, the image display device) with a retardation layer can be achieved. In this specification, an "orientation cured layer" means a layer in which a liquid crystal compound is oriented in a predetermined direction in the layer and the orientation state is fixed. It should be noted that the "orientation cured layer" is a concept including an orientation cured layer obtained by curing a liquid crystal monomer as described later. In the present embodiment, typically, it is preferable that rod-shaped liquid crystal compounds are oriented in a state of being arranged in the slow axis direction of the second retardation layer (homogeneous alignment). As the liquid crystal compound, for example, a liquid crystal compound having a nematic liquid crystal phase (nematic liquid crystal) can be cited. As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The mechanism for expressing the liquid crystallinity of the liquid crystal compound can be lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer can be used alone or in combination. In the case where the liquid crystal compound is a liquid crystalline monomer, it is preferably a polymerizable monomer and / or a crosslinkable monomer, for example. This is because by polymerizing or crosslinking the liquid crystalline monomer, the orientation state of the liquid crystalline monomer can be fixed. After the liquid crystalline monomer is oriented, for example, if the liquid crystalline monomers are polymerized or crosslinked with each other, the above-mentioned orientation state can be fixed thereby. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by crosslinking, but they are non-liquid crystalline. Therefore, the formed first retardation layer does not undergo, for example, a transition to a liquid crystal phase, a glass phase, or a crystalline phase due to a temperature change peculiar to a liquid crystal compound. As a result, the formed first retardation layer can be a retardation layer that is extremely excellent in stability and is not affected by temperature changes. The first retardation layer may be a laminate having a liquid crystal alignment cured layer formed on an arbitrary appropriate substrate. The laminate having a liquid crystal alignment cured layer formed on the substrate may be directly laminated with other optical functional films, or the liquid crystal alignment cured layer may be transferred onto other optical functional films (such as a polarizer, a polarizing plate including a polarizer, etc.) and laminated. Specific examples of the substrate include polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cyclic polyolefins such as norbornene-based polymers; cellulose-based polymers such as diacetate cellulose and triacetate cellulose; acrylic polymers; styrene polymers; polycarbonates, polyamides, polyimides, etc. The substrate preferably has an orientation restricting force that causes liquid crystal molecules to be oriented in a specified direction. Representative of the orientation restricting force can be imparted by rubbing orientation, stretching substrate orientation, or photoorientation. The orientation restricting force is preferably imparted by stretching substrate orientation or photoorientation. Specific examples of the liquid crystal compound and details of the method for forming the liquid crystal alignment cured layer are described, for example, in Japanese Patent Application Laid-Open No. 2006-163343 and Japanese Patent Application Laid-Open No. 2006-178389. The descriptions in these publications are incorporated herein by reference. As described above, the first retardation layer may be a stretched film of a polymer film. As the resin for forming the polymer film, any appropriate resin can be used. Specific examples include resins that form a positive birefringent film such as cyclic olefin-based resins, polycarbonate-based resins, cellulose-based resins, polyvinyl alcohol-based resins, and polysulfone-based resins. Among them, cyclic olefin-based resins (such as norbornene-based resins) and polycarbonate-based resins are preferred. The above-mentioned norbornene-based resin is a resin polymerized with norbornene-based monomers as polymerization units. Examples of the norbornene-based monomers include norbornene, and its alkyl and / or alkylene substituents, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylene-2-norbornene, etc., and their polar group substituents such as halogens; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; dimethanooctahydronaphthalene, its alkyl and / or alkylene substituents, and polar group substituents such as halogens, such as 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, etc.; 3-4 polymers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-H-benzindene, 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentanthracene. The above-mentioned norbornene-based resin may be a copolymer of a norbornene-based monomer and other monomers. The above-mentioned polycarbonate-based resin contains, for example, structural units derived from fluorene-based dihydroxy compounds, structural units derived from isosorbide-based dihydroxy compounds, and structural units derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, diethylene glycol, triethylene glycol or polyethylene glycol, and alkylene diols or spiro diols. The polycarbonate-based resin preferably contains structural units derived from fluorene-based dihydroxy compounds, structural units derived from isosorbide-based dihydroxy compounds, and structural units derived from spiro diols. The polycarbonate-based resin may contain structural units derived from other dihydroxy compounds as needed. It should be noted that the details of the polycarbonate-based resin suitable for use in the present invention are described, for example, in Japanese Patent Application Laid-Open No. 2014-10291, Japanese Patent Application Laid-Open No. 2014-26266, Japanese Patent Application Laid-Open No. 2015-212816, Japanese Patent Application Laid-Open No. 2015-212817, Japanese Patent Application Laid-Open No. 2015-212818, and this description is incorporated herein by reference. The retardation film (stretched film) corresponding to the first retardation layer can be obtained by stretching the above-mentioned polymer film under any appropriate stretching conditions. Specifically, by appropriately selecting the type of polymer, stretching conditions (such as stretching temperature, stretching ratio, stretching direction), and stretching method (such as longitudinal uniaxial stretching), a retardation film (first retardation layer) having the above-mentioned desired optical properties (such as refractive index properties, in-plane retardation, retardation in the thickness direction) can be obtained. In particular, by adjusting the thickness of the polymer film (blank thickness), stretching temperature, and stretching ratio, the Re 1 (550) can be adjusted to within the above range. The thickness of the first retardation layer can be set in a manner that obtains the desired optical properties. When the first retardation layer is a liquid crystal alignment cured layer, the lower limit of the thickness is preferably 0.5 μm or more. The upper limit of the thickness of the first retardation layer is preferably 10 μm or less, more preferably 8 μm or less, and still more preferably 5 μm or less. When the first retardation layer is a stretched film of a polymer film, the lower limit of the thickness of the first retardation layer is preferably 5 μm or more, more preferably 10 μm or more, and still more preferably 15 μm or more. The upper limit of the thickness of the first retardation layer is preferably 55 μm or less, more preferably 50 μm or less, and still more preferably 45 μm or less. D. Second retardation layer The range of the light transmittance at a wavelength of 550 nm of the second retardation layer is the same as the range of the light transmittance of the above-mentioned first retardation layer. The refractive index characteristics of the second retardation layer preferably exhibit a relationship of nx > ny = nz or nz > nx > ny. That is, the second retardation layer is preferably a positive A plate or a positive B plate. When the second retardation layer is a positive A plate, the constitution of the second retardation layer is as described above for the first retardation layer in item C. When the second retardation layer is a positive B plate, the second retardation layer is preferably composed of a resin film. If it has such a constitution, compared with the case where the retardation layer is a liquid crystal alignment layer, lamination is easier, and the mechanical strength of the optical laminate is excellent. The second retardation layer is typically composed of a stretched film of a polymer film mainly composed of a thermoplastic resin. As the thermoplastic resin, a polymer showing negative birefringence is preferably used. By using a polymer showing negative birefringence, a retardation film having a refractive index ellipsoid of nz > nx > ny can be easily obtained. Here, "showing negative birefringence" means that when the polymer is oriented by stretching or the like, the refractive index in the stretching direction becomes relatively smaller. In other words, it means that the refractive index in the direction orthogonal to the stretching direction becomes larger. As the polymer showing negative birefringence, for example, a polymer having a chemical bond or functional group with large polarization anisotropy such as an aromatic ring or a carbonyl group introduced into the side chain can be cited. Specifically, acrylic resins, styrene resins, maleimide resins, etc. can be cited. The above acrylic resin can be obtained, for example, by addition polymerization of an acrylate monomer. As the acrylic resin, for example, polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate can be cited. The above styrene resin can be obtained, for example, by addition polymerization of a styrene monomer. As the styrene monomer, for example, styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene, p-tert-butylstyrene can be cited. The above maleimide resin can be obtained, for example, by addition polymerization of a maleimide monomer. As the maleimide monomer, for example, N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(2-ethylphenyl)maleimide, N-(2-propylphenyl)maleimide, N-(2-isopropylphenyl)maleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-dipropylphenyl)maleimide, N-(2,6-diisopropylphenyl)maleimide, N-(2-methyl-6-ethylphenyl)maleimide, N-(2-chlorophenyl)maleimide, N-(2,6-dichlorophenyl)maleimide, N-(2-bromophenyl)maleimide, N-(2,6-dibromophenyl)maleimide, N-(2-biphenyl)maleimide, N-(2-cyanophenyl)maleimide can be cited. In the above addition polymerization, after polymerization, the birefringence characteristics of the obtained resin can also be controlled by substituting the side chain, or by causing a maleimidation, grafting reaction, etc. The polymers showing negative birefringence described above can be copolymerized with other monomers. By copolymerizing with other monomers, brittleness, moldability, and heat resistance can be improved. Examples of such other monomers include olefins such as ethylene, propylene, 1-butene, 1,3-butadiene, 2-methyl-1-butene, 2-methyl-1-pentene, 1-hexene; acrylonitrile; (meth)acrylates such as methyl acrylate and methyl methacrylate; maleic anhydride; vinyl esters such as vinyl acetate. When the polymer showing negative birefringence described above is a copolymer of the styrene-based monomer and the other monomer, the blending ratio of the styrene-based monomer is preferably 50 mol% to 80 mol%. When the polymer showing negative birefringence described above is a copolymer of the maleimide-based monomer and the other monomer, the blending ratio of the maleimide-based monomer is preferably 2 mol% to 50 mol%. By blending within such a range, a polymer film excellent in toughness and moldability can be obtained. As the polymer showing negative birefringence described above, it is preferable to use a styrene-maleic anhydride copolymer, a styrene-acrylonitrile copolymer, a styrene-(meth)acrylate copolymer, a styrene-maleimide copolymer, a vinyl ester-maleimide copolymer, an olefin-maleimide copolymer, etc. They can be used alone or in combination of two or more. These polymers show high negative birefringence and excellent heat resistance. These polymers can be obtained, for example, from NOVACHEMICAL JAPAN and Arakawa Chemical Industries, Ltd. As the polymer showing negative birefringence described above, it is also preferable to use a polymer having a repeating unit represented by the following general formula (I). Such a polymer shows higher negative birefringence and excellent heat resistance and mechanical strength. Such a polymer can be obtained, for example, by using an N-phenyl-substituted maleimide in which the N-substituent of a maleimide-based monomer having a phenyl group substituted at least in the ortho position is introduced as a starting material. In the above general formula (I), R 1 ~R 5 each independently represent hydrogen, a halogen atom, a carboxylic acid, a carboxylic acid ester, a hydroxyl group, a nitro group, or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms (wherein R 1 and R 5 are not simultaneously hydrogen atoms), R 6 and R 7 represent hydrogen or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms, and n represents an integer of 2 or more. As the polymer exhibiting negative birefringence described above, it is not limited thereto. For example, a cyclic olefin copolymer disclosed in Japanese Patent Application Laid-Open No. 2005-350544 or the like may also be used. Further, a composition containing a polymer and inorganic fine particles disclosed in Japanese Patent Application Laid-Open No. 2005-156862, Japanese Patent Application Laid-Open No. 2005-227427 or the like may also be suitably used. In addition, as the polymer exhibiting negative birefringence, one kind may be used alone, or two or more kinds may be used in combination. Further, they may be used after being modified by copolymerization, branching, crosslinking, molecular end modification (or capping), and stereoregular modification or the like. The above-mentioned polymer thin film may further contain any appropriate additive as needed. Specific examples of the additive include a plasticizer, a heat stabilizer, a light stabilizer, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, an antistatic agent, a compatibilizer, a crosslinking agent, a thickener and the like. The type and content of the additive may be appropriately set according to the purpose. The content of the additive is typically about 3 to 10 parts by weight with respect to 100 parts by weight of the total solid content of the polymer thin film. If the content of the additive is too large, the transparency of the polymer thin film may be impaired, or the additive may ooze out from the surface of the polymer thin film. As the method for forming the above-mentioned polymer thin film, any appropriate forming method may be adopted. For example, a compression molding method, a transfer molding method, an injection molding method, an extrusion molding method, a blow molding method, a powder molding method, an FRP molding method, a solvent casting method and the like can be cited. Among them, an extrusion molding method and a solvent casting method are preferably used. This is because a retardation film having high smoothness and good optical uniformity can be obtained. Specifically, the extrusion molding method is as follows: a resin composition containing the above-mentioned thermoplastic resin, plasticizer, additive and the like is heated to be melted, and is extruded in a film shape through a T-die or the like onto the surface of a casting roll, and is cooled to be formed into a film. The solvent casting method is as follows: a thick solution (concentrate) obtained by dissolving the above-mentioned resin composition in a solvent is defoamed, and is uniformly cast in a film shape on the surface of a metallic endless belt or a rotating drum, or a plastic substrate or the like, and the solvent is evaporated to be formed into a film. It should be noted that the molding conditions can be appropriately set according to the composition, type, molding process method and the like of the resin used. As the method for forming the above-mentioned polymer thin film, any appropriate forming method may be adopted. The molding conditions can be appropriately set according to the composition, type, molding process method and the like of the resin used. The retardation film (stretched film) corresponding to the second retardation layer can be obtained by stretching the above-mentioned polymer thin film under any appropriate stretching conditions. As specific examples of the stretching method, a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a sequential biaxial stretching method in the longitudinal and transverse directions, and a simultaneous biaxial stretching method in the longitudinal and transverse directions can be cited. The longitudinal uniaxial stretching method, the sequential biaxial stretching method in the longitudinal and transverse directions, and the simultaneous biaxial stretching method in the longitudinal and transverse directions are preferably used. In the above polymer showing negative birefringence, as described above, the refractive index in the stretching direction relatively decreases. Therefore, in the case of the longitudinal uniaxial stretching method, the fast axis is in the conveying direction of the polymer thin film (the refractive index in the direction orthogonal to the conveying direction is nx). In the case of the sequential biaxial stretching method in the longitudinal and transverse directions and the simultaneous biaxial stretching method in the longitudinal and transverse directions, depending on the ratio of the stretching ratios in the longitudinal and transverse directions, both the conveying direction and the width direction can be the slow axes. Specifically, if the stretching ratio in the longitudinal (conveying) direction is relatively increased, the transverse (width) direction becomes the slow axis, and if the stretching ratio in the transverse (width) direction is relatively increased, the longitudinal (conveying) direction becomes the slow axis. By adjusting the thickness of the polymer thin film (blank thickness), the stretching temperature, and the stretching ratio, the Re of the second retardation layer 2 (550) and the Nz coefficient can be adjusted to the above ranges. The stretching temperature (the temperature in the stretching oven when stretching the polymer thin film) is preferably near the glass transition temperature (Tg) of the polymer thin film. Specifically, it is preferably (Tg - 10) °C to (Tg + 30) °C, more preferably Tg to (Tg + 25) °C, and particularly preferably (Tg + 5) °C to (Tg + 20) °C. When the stretching temperature is too low, there is a concern that the phase difference value and the direction of the slow axis become uneven, or the polymer thin film crystallizes (becomes cloudy). On the other hand, if the stretching temperature is too high, there is a concern that the polymer thin film melts or the expression of the phase difference becomes insufficient. It should be noted that the glass transition temperature can be determined by the DSC method according to JIS K7121-1987. Any suitable method can be adopted for the above method of controlling the temperature in the stretching oven. For example, an air circulation type constant temperature oven using hot air or cold air circulation, a heater using microwaves or far-infrared rays, a roller heated to adjust the temperature, a heat pipe roller, or a metal belt can be cited. The stretching ratio can be set to any appropriate value according to the composition of the polymer thin film, the types of volatile components, etc., the residual amount of volatile components, etc., and the desired phase difference value. For example, from the viewpoints of the mechanical accuracy and stability of the stretching device, etc., the conveying speed during stretching is preferably 0.5 m / minute to 20 m / minute. As described above, a method for obtaining a retardation film using a polymer exhibiting negative birefringence has been described. However, a retardation film can also be obtained using a polymer exhibiting positive birefringence. As a method for obtaining a retardation film using a polymer exhibiting positive birefringence, for example, a stretching method that increases the refractive index in the thickness direction, such as those disclosed in JP-A-2000-231016, JP-A-2000-206328, and JP-A-2002-207123, can be used. Specifically, a method of bonding a heat-shrinkable film to one or both sides of a film containing a polymer exhibiting positive birefringence and performing a heat treatment can be cited. By causing the film to shrink under the action of the shrinkage force of the heat-shrinkable film based on the heat treatment, and causing the length direction and width direction of the film to shrink, the refractive index in the thickness direction can be increased, and a positive B plate can be obtained. In this way, a positive B plate can also be manufactured using a polymer exhibiting either positive or negative birefringence. Generally, when using a polymer exhibiting positive birefringence, it has an advantage in terms of a large variety of selectable polymers. When using a polymer exhibiting negative birefringence, compared with the case of using a polymer exhibiting positive birefringence, due to its stretching method, it has an advantage in easily obtaining a retardation film with excellent uniformity in the slow axis direction. The thickness of the second retardation layer can be set in such a way as to obtain desired optical characteristics. When the second retardation layer is a positive B plate, the thickness of the second retardation layer is preferably 1 μm or more, more preferably 4 μm or more. The thickness of the second retardation layer is typically 200 μm or less, preferably 150 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. E. Third retardation layer The range of the transmittance at a wavelength of 550 nm of the third retardation layer is the same as the range of the transmittance of the first retardation layer described above. The refractive index characteristics of the third retardation layer exhibit a relationship of nx > ny as described above, and preferably exhibit a relationship of nz > nx > ny, or nx > ny = nz. That is, the third retardation layer is preferably a positive B plate or a positive A plate. When the third retardation layer is a positive A plate, the third retardation layer is as described in item C above regarding the first retardation layer. When the third retardation layer is a positive B plate, the third retardation layer is as described in item D above regarding the case where the second retardation layer is a positive B plate. F. Image display device The optical laminate described in the above items A to E can be applied to an image display device. Therefore, embodiments of the present invention also include an image display device using such an optical laminate. Representative examples of the image display device include a liquid crystal display device, an organic EL display device, and the like. In particular, in an image display device to which the above optical laminate is applied, light leakage in the tilt direction can be reduced, and thus it can be suitably used for an organic EL display device. The image display device according to an embodiment of the present invention includes an image display panel and the optical laminate described in the above items A to E. Typically, the image display device includes an image display panel and the above optical laminate disposed on the visual recognition side of the image display panel. Example Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows. (1) Measurement of retardation For the retardation values of the first retardation layer, the second retardation layer, and the third retardation layer used in the examples and comparative examples, automatic measurement was performed using KOBRA-WPR manufactured by Oji Scientific Instruments Co., Ltd. The measurement wavelengths were 448.1 nm, 498.7 nm, 545.6 nm, 587.4 nm, and 628.8 nm, and the measurement temperature was 23°C. In addition, using an Abbe refractometer manufactured by Atago Co., Ltd., the average refractive index was measured, and the refractive indices nx, ny, and nz were calculated from the obtained retardation values. (2) Luminance (front luminance and oblique luminance in pure black display) Based on simulation, the luminance in the front direction and the tilt direction in pure black display of the optical laminates formed in the examples and comparative examples was evaluated. The simulation was performed using "LCDMASTER Ver.6.084" manufactured by Shintec Co., Ltd. (hereinafter, sometimes referred to as the simulation device), and the extended function of the simulation device was used. Specifically, the refractive index of each wavelength of each retardation layer was converted from the data obtained in (1) to prepare simulation data for the first retardation layer, the second retardation layer, and the third retardation layer. Retardation layers were selected in which the values of the front luminance and the deviation of the oblique luminance were below a certain level when the axes of the respective retardation layers were 0° to 180° and the retardation was 30 nm to 300 nm, and more detailed simulations were performed for each configuration. Based on the data obtained through the detailed simulation, the luminance in the front direction in pure black display was defined as the "front luminance". In addition, regarding the tilt direction, the luminance data at a polar angle of 60° and azimuth angles of 0° to 360° were extracted, and the maximum value of the luminance in the tilt direction was calculated as the "maximum tilt luminance", and the difference between the maximum value and the minimum value of the luminance in the tilt direction was calculated as the "tilt luminance deviation". (3) Hue For the hues in the front direction and the tilt direction during pure black display of the image display devices obtained in the examples and comparative examples, evaluation was performed based on simulation in the same manner as in (2) above. The simulation used the above-described simulation device and this extended function. Regarding the hue in the front direction, the distance between two points of the hue from the neutral point was evaluated. For the hue in the tilt direction, the distance between two points of the hue at a polar angle of 60° and azimuth angles of 0° to 360° was evaluated. Based on the obtained results, the a* value and b* value were calculated for the hue in the front direction during pure black display ("front hue"), and the Δa* value and Δb* value were calculated for the hue in the tilt direction ("oblique hue deviation"). [Production Example] (Production of Positive A Plate) <Production Examples A1 - A8> A photopolymerizable liquid crystal compound that exhibits a nematic liquid crystal phase ("Paliocolor LC242" manufactured by BASF) was dissolved in cyclopentanone to prepare a solution with a solid content concentration of 30% by weight. A surfactant ("BYK - 360" manufactured by BYK - Chemie) and a photopolymerization initiator ("Omnirad907" manufactured by IGM Resins) were added to this solution to prepare a liquid crystalline composition solution. The addition amounts of the leveling agent and the polymerization initiator were set to 0.01 part by weight and 3 parts by weight, respectively, relative to 100 parts by weight of the photopolymerizable liquid crystal compound. An obliquely stretched norbornene - based film ("ZEONOR FILM (ZD12)" manufactured by ZEON Corporation, Japan, thickness: 23 μm) was prepared, and the above - described liquid crystalline composition was coated on the obliquely stretched norbornene - based film using a bar coater so that the thickness after drying would be the thickness that could obtain the desired in - plane retardation shown in Table 1. It was heated at 100°C for 3 minutes to align the liquid crystals. After cooling to room temperature, ultraviolet rays with a cumulative light amount of 400 mJ / cm 2 were irradiated in a nitrogen atmosphere for photocuring, and a uniformly oriented liquid crystal layer was formed on the obliquely stretched norbornene - based film. Thus, a retardation layer showing the characteristics of each positive A plate of Production Examples A1 - A8 was obtained. <Production Example A9> 55 parts by weight of the compound represented by the following formula (I), 25 parts by weight of the compound represented by the following formula (II), and 20 parts by weight of the compound represented by the following formula (III) were added to 400 parts by weight of cyclopentanone (CPN), and then heated to 60 °C and stirred to dissolve. Then, the mixed solution of the above compounds was returned to room temperature, 3 parts by weight of Irgacure 907 (manufactured by BASF Japan), 0.2 parts by weight of Megafac F-554 (manufactured by DIC), and 0.1 parts by weight of p-methoxyphenol (MEHQ) were added to the mixed solution of the above compounds, and further stirred. The stirred solution was transparent and homogeneous. The obtained solution was filtered through a 0.20 μm membrane filter to obtain a polymerizable composition. In addition, an alignment film polyimide solution was coated on a glass substrate with a thickness of 0.7 mm by a spin coating method, dried at 100 °C for 10 minutes, and then fired at 200 °C for 60 minutes to obtain a coating film of polyimide for the alignment film. The obtained coating film was subjected to a rubbing treatment using a commercially available rubbing device to form an alignment film. Next, the above-obtained polymerizable composition was coated on a substrate (substantially an alignment film) by a spin coating method and dried at 100 °C for 2 minutes. After the coating film of the polymerizable composition obtained was cooled to room temperature, ultraviolet rays were irradiated for 30 seconds using a high-pressure mercury lamp at an intensity of 30 mW / cm 2 . Thus, a retardation layer (thickness: 2.7 μm) as an alignment cured layer of a liquid crystal compound was obtained. The in-plane retardation Re(550) of the retardation layer is shown in Table 1. In addition, Re(450) / Re(550) of the retardation layer was 0.851, showing an abnormal dispersion wavelength characteristic. (Production of positive B plate) <Production Example B1> Using a single-screw extruder and a T-die head, granular resin of a styrene-maleic anhydride copolymer (manufactured by NOVACHEMICAL JAPAN, trade name "DYRARC D232") was extruded at 270 °C, and the sheet-like molten resin was cooled with a cooling drum to obtain a film with a thickness of 40 μm. The film (thickness: 40 μm) was longitudinally stretched at the free end in the conveying direction at 130 °C so that the in-plane retardation Re(550) was the value shown in Table 1 to obtain a retardation film. The retardation film thus obtained was a positive B plate in which the refractive index characteristics showed the relationship of nz > nx > ny. The Nz coefficient of the positive B plate is shown in Table 1. <Production Examples B2 - B3> The film before stretching (thickness: 40 μm) produced in Production Example B1 was longitudinally stretched freely at 130°C in the transport direction so that the in-plane retardation Re(550) and the Nz coefficient had the values shown in Table 1, thereby obtaining a retardation film. (Production of positive C-plate) (Production Examples C1 - C2) Regarding Production Example C1 and Production Example C2, the retardation Rth 3 (550) was changed to 80 nm, and otherwise, a retardation film was obtained in the same manner as in Production Example 6 of Japanese Patent No. 6896118. The retardation film thus obtained is a positive C-plate in which the refractive index characteristics show the relationship nz > nx = ny. It should be noted that, as shown in Table 1, the retardation films of the above respective production examples were classified into a first retardation film corresponding to the first retardation layer, a second retardation film corresponding to the second retardation layer, and a third retardation film corresponding to the third retardation layer. (Production of polarizer) (Production Example P1) As a thermoplastic resin substrate, an amorphous isophthalic acid copolyethylene terephthalate film (thickness: 100 μm) in a long strip shape with a Tg of about 75°C was used, and corona treatment was performed on one side of the resin substrate. 13 parts by mass of potassium iodide was added to 100 parts by mass of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name “GOHSEFIMER”) in a ratio of 9:1, and the resulting product was dissolved in water to prepare a PVA aqueous solution (coating solution). The above PVA aqueous solution was coated on the corona-treated surface of the resin substrate and dried at 60°C, thereby forming a PVA-based resin layer with a thickness of 13 μm to produce a laminate. The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (length direction) in an oven at 130°C (air-assisted stretching treatment). Next, the laminate was immersed in a insolubilizing bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by blending 4 parts by mass of boric acid with 100 parts by mass of water) for 30 seconds (insolubilizing treatment). Next, in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by blending iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by mass of water), it was immersed for 60 seconds while adjusting the concentration so that the monomer transmittance (Ts) of the finally obtained polarizer became the desired value (dyeing treatment). Next, it was immersed for 30 seconds (crosslinking treatment) in a crosslinking bath at a liquid temperature of 40°C (an aqueous boric acid solution prepared by compounding 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with 100 parts by mass of water). Then, while immersing the laminate in an aqueous boric acid solution (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70°C, it was uniaxially stretched (stretching treatment in water) in the longitudinal direction (length direction) between rollers with different circumferential speeds so that the total stretching ratio became 5.5 times. Then, the laminate was immersed in a cleaning bath at a liquid temperature of 20°C (an aqueous solution prepared by compounding 4 parts by mass of potassium iodide with 100 parts by mass of water) (cleaning treatment). Then, while drying in an oven maintained at about 90°C, it was brought into contact with a SUS-made heating roller having a surface temperature maintained at about 75°C (dry shrinkage treatment). Through the above operations, a polarizer with a thickness of about 5 μm was formed on the resin substrate, and a laminate having a structure of resin substrate / polarizer was obtained. An HC-TAC film (thickness: 20 μm) was adhered as a protective layer to the surface of the polarizer (the surface opposite to the resin substrate) of the obtained laminate. Then, the resin substrate was peeled off to obtain a polarizing plate having a structure of HC-TAC film / polarizer / . [Example 1] A polarizing plate of Production Example P1 was prepared, a retardation film of Production Example A1 was prepared as the first retardation film, a retardation film of Production Example B1 was prepared as the second retardation film, and a retardation film of Production Example A2 was prepared as the third retardation film. For each retardation film, the retardation value was measured based on the above (1). Next, optical characteristic data and refractive index data of each of the first retardation layer, the second retardation layer, and the third retardation layer were obtained by simulation. Data of each retardation layer were created using a simulation device, and the simulation was performed 3 times. In the first simulation, using the extended function of the simulation device, a cyclic simulation was performed in which the axes of the respective retardation layers were incremented by 15° in the range of 0° to 180° and the retardation was incremented by 30 nm in the range of 30 nm to 300 nm. Numerical values of the front luminance, the front hue, the oblique luminance and the hue at a polar angle of 60° at azimuth angles of 0°, 45°, 90°, and 135° were respectively extracted, and the optimal structure of the optical laminate formed by sequentially laminating the first retardation layer, the second retardation layer, and the third retardation layer was determined. In the second simulation, based on the optimal structure of the optical laminate in the first simulation above, using the extended function of the simulation device, it was performed with an increment of 1° in the range of ±15° of the axis angle and an increment of 1 nm in the range of ±30 nm of the retardation. The same data analysis as in the first simulation was performed. In the third simulation, for the laminate that was the best value among the values obtained in the second simulation, using the simulation apparatus, while changing the Nz coefficient of the second retardation layer, the optimization of the Nz coefficient was performed. The equal-contrast curve distributions of the viewing angles during black display of the optical laminate obtained by performing three simulations are shown in Figure 2A . [Example 2-3 and Comparative Example 1] The first retardation film, the second retardation film, the third retardation film, and the angles formed by the slow axes of the respective retardation films and the absorption axis of the polarizer of the polarizer ("the angle formed by the absorption axis and the slow axis") were changed as shown in Table 1. Other than that, the simulation was performed in the same manner as in Example 1. The results are shown in Table 1. In addition, Figure 2B and Figure 2C respectively show the equal-contrast curve distributions of the viewing angles during pure black display of Example 2 and Example 3. The equal-contrast curve distribution of the viewing angle during pure black display of Comparative Example 1 is shown in Figure 3A . [Comparative Example 2] The first retardation film, the second retardation film, and the angles formed by the slow axes of the respective retardation films and the absorption axis of the polarizer ("the angle formed by the absorption axis and the slow axis") were changed as shown in Table 1, and the third retardation film was not used. Other than that, the simulation was performed in the same manner as in Example 1. The results are shown in Table 1. The equal-contrast curve distribution of the viewing angle during pure black display of Comparative Example 2 is shown in Figure 3B . [Table 1] [Evaluation] From the results in Table 1 and the Figures 2A to 3B equal-contrast curve distribution diagrams of the viewing angles, it can be seen that in an optical laminate including a polarizer having a polarizer, a first retardation layer, a second retardation layer, and a third retardation layer, by making at least one of the second retardation layer and the third retardation layer a retardation layer in which the refractive index characteristics show the relationship nz > nx > ny, the deviation of the luminance in the tilt direction (polar angle 60°) during pure black display can be suppressed to a low level. That is, it can be seen that if at least one of the second retardation layer and the third retardation layer is a positive B plate, it can contribute to suppressing the deviation of the luminance in the tilt direction during pure black display. As a result, if an optical laminate satisfying the above conditions is adopted in an image display device, an image display device with suppressed light leakage in the tilt direction can be realized. Industrial Applicability The optical laminate of the embodiment of the present invention can be suitably applied to an image display device (typically a liquid crystal display device, an organic EL display device).

Claims

1. An optical laminate comprising, in order, a polarizing plate including a polarizer, a first phase difference layer, a second phase difference layer, and a third phase difference layer, The refractive index characteristic of at least one of the second retardation layer and the third retardation layer shows a relationship of nz>nx>ny.

2. The optical layered body according to claim 1, wherein: The refractive index characteristic of the first phase difference layer shows a relationship of nx>ny=nz.

3. The optical laminate according to claim 2, wherein: The refractive index characteristic of the retardation layer of either the second retardation layer or the third retardation layer shows the relationship of nx>ny=nz.

4. The optical laminate according to claim 3, wherein: The refractive index characteristics of the second phase difference layer show the relationship of nz>nx>ny. The in-plane phase difference Re of the first phase difference layer 1 (550) is greater than or equal to 130 nm and less than or equal to 150 nm, The in-plane phase difference Re of the second phase difference layer 2 (550) is greater than or equal to 140 nm and less than or equal to 160 nm, The in-plane phase difference Re of the third phase difference layer 3 (550) is greater than 190 nm and less than 210 nm, The angle between the absorption axis of the polarizer and the slow axis of the first phase difference layer is greater than or equal to 13.5° and less than or equal to 33.5°. The angle between the absorption axis of the polarizer and the slow axis of the second phase difference layer is greater than or equal to -10° and less than or equal to 10°. An angle formed by the absorption axis of the polarizer and the slow axis of the third retardation layer is greater than or equal to 62.5° and less than or equal to 82.5°.

5. The optical layered body according to claim 3, wherein: The refractive index characteristics of the third phase difference layer show the relationship of nz>nx>ny. The in-plane phase difference Re of the first phase difference layer 1 (550) is greater than 185 nm and less than 205 nm, The in-plane phase difference Re of the second phase difference layer 2 (550) is greater than or equal to 110 nm and less than or equal to 130 nm, The in-plane phase difference Re of the third phase difference layer 3 (550) is greater than or equal to 50 nm and less than or equal to 70 nm, The angle between the absorption axis of the polarizer and the slow axis of the first phase difference layer is greater than or equal to 0° and less than or equal to 20°. The angle between the absorption axis of the polarizer and the slow axis of the second phase difference layer is greater than or equal to 30° and less than or equal to 50°. An angle formed between the absorption axis of the polarizer and the slow axis of the third retardation layer is greater than or equal to 80° and less than or equal to 100°.

6. The optical layered body according to claim 1, wherein: The phase difference layer whose refractive index characteristic shows the relationship of nz>nx>ny is composed of a resin film. 7 . An image display device comprising an image display panel and the optical layered body according to claim 1 .

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