Optical laminate and image display device

Abstract

To provide an optical laminate that can prevent leakage of light in an oblique direction.SOLUTION: An optical laminate according to the present embodiment comprises a polarizing plate including a polarizer, a first phase difference layer, a second phase difference layer, and a third phase difference layer, in this order. At least one phase difference layer of the second phase difference layer and the third phase difference layer has refractive index characteristics indicating the relationship of nz>nx>ny.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical laminate and an image display device.

Background Art

[0002] In image display devices such as organic electroluminescence (EL) display devices, various optical laminates combining a polarizing plate and an optical compensation film are used to achieve optical characteristics suitable for the application (for example, Patent Document 1). For example, an optical laminate has been proposed in which a retardation layer having a refractive index characteristic of nx > ny = nz, a retardation layer having a refractive index characteristic of nz > nx = ny, and a retardation layer having a refractive index characteristic of nx > ny ≥ nz are stacked in this order on a polarizing plate including a polarizer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in an image display device using the optical laminate as described above, light leakage tends to occur in an oblique direction. An object of the present invention is to provide an optical laminate capable of realizing an image display device in which light leakage in an oblique direction is suppressed.

Means for Solving the Problems

[0005] [1] The optical laminate according to an embodiment of the present invention includes a polarizing plate including a polarizer, a first retardation layer, a second retardation layer, and a third retardation layer in this order. At least one of the second retardation layer and the third retardation layer has a refractive index characteristic of nz > nx > ny. [2] In the optical laminate described in [1] above, the refractive index characteristics of the first retardation layer may exhibit the relationship nx > ny = nz. [3] In the optical laminate described in [1] or [2] above, either one of the second retardation layer or the third retardation layer may have refractive index characteristics showing the relationship nx > ny = nz. [4] In the optical laminate according to any one of [1] to [3] above, the second retardation layer may have refractive index characteristics showing the relationship nz > nx > ny. 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. 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. [5] In the optical laminate according to any one of [1] to [3] above, the third retardation layer may have refractive index characteristics showing the relationship nz > nx > ny. 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. 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. [6] In the optical laminate according to any one of [1] to [5] above, the retardation layer having the refractive index characteristics showing the relationship nz > nx > ny may be composed of a resin film. [7]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.

Effect of the Invention

[0006] According to an embodiment of the present invention, there is provided an optical laminate capable of realizing an image display device in which light leakage in an oblique direction is suppressed.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 3A

Figure 3B

Modes for Carrying Out the Invention

[0008] Hereinafter, representative embodiments of the present invention will be described, but the present invention is not limited to these embodiments. In this specification, the expression "A and / or B" means any one of "A and B", "A", or "B".

[0009] (Definition of Terms and Symbols) The definitions of terms and symbols in this specification are as follows. (1) Refractive Index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (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 (film) is d (nm), Re(λ) is obtained by the formula: Re(λ) = (nx - ny) × d. In this specification, 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」 may be 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 (film) is d (nm), Rth(λ) is obtained by the formula: Rth(λ) = (nx - nz) × d. In this specification, the 「retardation in the thickness direction Rth(λ) of the first retardation layer」 is 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」 may be referred to as 「Rth 3 (λ)」. (4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re. (5) Substantially parallel or orthogonal The expressions "substantially orthogonal" and "substantially perpendicular" include the case where the angle formed by two directions is 90° ± 3°, and the expressions "substantially parallel" and "substantially parallel" include the case where the angle formed by two directions is 0° ± 3°. Further, "intersecting without being substantially orthogonal" means that the angle formed by two directions is neither substantially orthogonal nor substantially parallel. More specifically, the expression "intersecting without being substantially orthogonal" includes the case where the angle formed by two directions exceeds 3° and is less than 87°, and the case 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 referring to an angle 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 (film) exhibiting a refractive index characteristic of nz > nx > ny may be referred to as a "positive B plate", a layer (film) exhibiting a refractive index characteristic of nx > ny = nz may be referred to as a "positive A plate", a layer (film) exhibiting a refractive index characteristic of nz > nx = ny may be referred to as a "positive C plate", and a layer (film) exhibiting a refractive index characteristic of nx > ny > nz may be referred to as a "negative B plate". Note 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".

[0010] A. Overall configuration of the optical laminate FIG. 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. The optical laminate 100 in the illustrated example includes a polarizing plate 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 viewing side, and the lower side of the drawing is the image display panel side. The polarizing plate 40 includes a polarizer 41 and a protective layer 42 disposed on one side of the polarizer 41 (the viewing side in the illustrated example). The polarizing plate 40 in the illustrated example is a so-called single-protection polarizing plate. Depending on the purpose, another protective layer (inner protective layer: not shown) may be disposed on the side opposite to the protective layer 42 of the polarizer 41. That is, the polarizing plate may be a double-protection polarizing plate. From the viewpoint of thinning the optical laminate, the inner protective layer can be omitted.

[0011] In the illustrated example, the first retardation layer 10 is disposed adjacent to the polarizing plate 40. More specifically, the first retardation layer 10 is disposed adjacent to the polarizer 41. As used herein, “disposed adjacent” means being directly laminated or laminated via only an adhesive layer (for example, an adhesive layer or an adhesive agent layer). That is, it means that no layer having other optical functions (hereinafter, may be referred to as an “optical function layer”) is interposed between the polarizing plate 40 and the first retardation layer 10. In the illustrated example, the second retardation layer 20 is disposed on the side opposite to the polarizing plate 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.

[0012] In an embodiment of the present invention, at least one of the second retardation layer 20 and the third retardation layer 30 has a refractive index characteristic showing a relationship of nz>nx>ny. With such a configuration, when the optical laminate is applied to an image display device, variations in luminance in an oblique direction in black display can be suppressed. As a result, in the image display device, the optical laminate can suppress light leakage in an oblique direction while maintaining a low luminance in the front direction in black display.

[0013] In a conventional optical laminate, when viewed from a specific azimuth angle in an oblique direction, there is an azimuth angle range where the luminance in black display becomes relatively large, resulting in luminance variation. As a result, when the conventional optical laminate is applied to an image display device, light leakage tends to occur. On the other hand, in the optical laminate according to an embodiment of the present invention, since the occurrence of luminance variation in the oblique direction in black display can be suppressed, it is considered that when the optical laminate is applied to an image display device, light leakage in the oblique direction can be suppressed. The reason for this is not necessarily clear, but the following mechanism is presumed. Usually, in an optical laminate including a plurality of retardation layers, the refractive index anisotropy of the laminate when each retardation layer is added together forms a refractive index ellipsoid. In this ellipsoid, when the azimuth angle is changed, the cross-sectional shape can vary depending on the angle. As a result, a difference in luminance (i.e., luminance variation) can occur depending on the viewing angle of the ellipsoid. On the other hand, according to the optical laminate according to an embodiment of the present invention, the cross-sectional shape of the ellipsoid formed by adding the retardation layers can be close to a perfect circle, so that even when the azimuth angle is changed (even when the viewing angle is changed), the difference in cross-sectional shape due to the angle can be reduced. As a result, it is presumed that the difference in luminance at each azimuth angle becomes small and the luminance variation becomes small. Note that the above is only a presumed mechanism and does not restrict or limit the present invention. Therefore, according to the optical laminate of the embodiment of the present invention, an image display device having excellent viewing angle dependency can be realized. Note that the luminance in the oblique direction in black display can be obtained, for example, by measuring the luminance while changing the azimuth angle in 5° increments at a polar angle of 60°. The method for measuring "luminance" and the measurement conditions will be described in detail in the section of Examples below.

[0014] As described above, at least one of the second retardation layer 20 and the third retardation layer 30 may have a refractive index characteristic showing the relationship of nz > nx > ny. Preferably, the refractive index characteristic of either the second retardation layer 20 or the third retardation layer 30 shows the relationship of nz > nx > ny.

[0015] The first retardation layer 10 preferably exhibits a refractive index characteristic of nx > ny = nz. In this case, preferably, one of the second retardation layer 20 and the third retardation layer exhibits a refractive index characteristic of nz > nx > ny, and the other exhibits a refractive index characteristic 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.

[0016] When the refractive index characteristic of the third retardation layer 30 exhibits a relationship of nz > nx > ny, preferably, both the refractive index characteristic of the first retardation layer 10 and the refractive index characteristic of the second retardation layer 20 exhibit a relationship of 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, the variation in the luminance in the diagonal direction in the black display of the optical laminate can be suppressed more favorably. Furthermore, it is less likely to affect the hue change in the front direction in the black display of the optical laminate, and the variation in the hue change in the diagonal direction in the black display can also be suppressed.

[0017] When the refractive index characteristic of the second retardation layer 20 exhibits a relationship of nz > nx > ny, preferably, both the refractive index characteristic of the first retardation layer 10 and the refractive index characteristic of the third retardation layer 30 exhibit a relationship of 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, the variation in the luminance in the diagonal direction in the black display of the optical laminate can be suppressed more favorably. Furthermore, it is less likely to affect the hue change in the front direction in the black display of the optical laminate, and the variation in the hue change in the diagonal direction in the black display can also be suppressed more favorably. It is presumed that the reason why not only the variation in the luminance in the diagonal direction in the black display but also the variation in the hue change in the diagonal direction in the black display is suppressed is that, in such a configuration, the cross-sectional shape when viewed from each azimuth angle direction of the refractive index ellipsoid when the refractive indices of the retardation layers are added together approaches a perfect circle more closely.

[0018] The optical laminate 100 may be in a sheet form or a long strip form. In this specification, the term "long strip form" means an elongated shape in which the length is sufficiently longer than the width, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more, the width. The long-strip optical laminate can be wound into a roll.

[0019] Practically, an adhesive layer (not shown) is provided on the side opposite to the polarizing plate 40 of the third retardation layer 30, and the optical laminate 100 is configured to be attachable to an image display. Further, it is preferable that a release liner is temporarily attached to the surface of the adhesive layer until the optical laminate 100 is put into use. By temporarily attaching the release liner, the adhesive layer is protected and roll formation becomes possible.

[0020] 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 indicating the refractive index characteristics of nz>nx>ny within a specific range, the optical laminate according to the embodiment of the present invention can exhibit a more remarkable effect.

[0021] A-1. The First Optical Laminate In one embodiment, the refractive index characteristics of the first retardation layer show the relationship of nx>ny=nz, the refractive index characteristics of the second retardation layer show the relationship of nz>nx>ny, and the refractive index characteristics of the third retardation layer show the 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. Such an optical laminate may be referred to as the "first optical laminate". According to the first optical laminate, when the optical laminate is applied to an image display device, the variation in the luminance in the diagonal direction in black display can be suppressed more favorably. As a result, when the first optical laminate is applied to an image display device, light leakage in the diagonal direction can be further suppressed.

[0022] 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.

[0023] 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. Incidentally, the "angle formed by the absorption axis of the polarizer and the slow axis of the first retardation layer" may be 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.

[0024] In the first optical laminate, when Re 1 (550) and / or the slow axis angle of the first retardation layer is within the above range, the variation in the luminance in the diagonal direction in the black display can be further suppressed. As a result, when the first optical laminate is applied to an image display device, light leakage in the diagonal direction can be further suppressed. That is, the effects according to the embodiments of the present invention can be remarkably achieved.

[0025] 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.

[0026] 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, and more preferably -0.25 or more and -0.05 or less. When the Nz coefficient of the second retardation layer is within the above range, the refractive index ellipsoid obtained by summing the refractive indices of the respective retardation layers in the first optical laminate can have a cross-sectional shape that is closer to a perfect circle when viewed from each azimuth angle direction. As a result, in the first optical laminate, variations in the luminance in the oblique direction in black display can be particularly suppressed.

[0027] 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, still more 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 may be, for example, 0°.

[0028] In the first optical laminate, Re 2 (550) and / or when the slow axis angle of the second retardation layer is within the above range, the effects according to the embodiments of the present invention can be exhibited more remarkably.

[0029] 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 still more 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 still more preferably 206 nm or less.

[0030] 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 still more preferably 67.5° or more and 77.5° or less.

[0031] In the first optical laminate, Re 3 (550) and / or when the slow axis angle of the third retardation layer is within the above range, the effects according to the embodiments of the present invention can be exhibited more remarkably.

[0032] A-2. Second optical laminate In one embodiment, the refractive index characteristic of the first retardation layer shows a relationship of nx>ny=nz, the refractive index characteristic of the second retardation layer shows a relationship of nx>ny=nz, and the refractive index characteristic of the third retardation layer shows 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. An optical laminate including such a combination of the first retardation layer, the second retardation layer, and the third retardation layer may be referred to as a "second optical laminate." According to the second optical laminate, the variation in luminance in the oblique direction in black display of the optical laminate can be further suppressed. As a result, when the second optical laminate is applied to an image display device, light leakage in the oblique direction can be further suppressed.

[0033] In the second optical laminate, the in-plane retardation Re of the first retardation layer 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. 1 (550) is preferably 205 nm or less, more preferably 203 nm or less, and further preferably 200 nm or less.

[0034] 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, even more preferably 5° or more and 15° or less, and particularly preferably 8° or more and 13° or less.

[0035] In the second optical laminate, Re 1 When the (550) and / or the slow axis angle of the first retardation layer is within the above range, the effects of the embodiment of the present invention can be significantly exhibited.

[0036] 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 even more 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 even more preferably 125 nm or less.

[0037] 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 even more preferably 37.5° or more and 47.5° or less.

[0038] In the second optical laminate, Re 2 When (550) and / or the slow axis angle of the second retardation layer is within the above range, the effects according to the embodiments of the present invention can be remarkably exhibited.

[0039] 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 even more 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 even more preferably 63 nm or less.

[0040] 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.

[0041] 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 even more preferably 87.5° or more and 92.5° or less. The slow axis angle of the third retardation layer may be, for example, 90°.

[0042] In the second optical laminate, Re 3 When (550) and / or the slow axis angle of the third retardation layer is within the above range, the second optical laminate can exhibit more remarkable effects.

[0043] As a representative example, the case where the first retardation layer is a positive A plate and one of the second retardation layer or the third retardation layer is a positive B plate has been described. However, the configuration of the optical laminate according to the embodiment of the present invention is not limited thereto. For example, the first retardation layer may be a positive A plate, and both the second retardation layer and the third retardation layer may be positive B plates. Further, within a range not departing from the object 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 may have any appropriate refractive index characteristics and slow axis angles according to the object. In the optical laminate according to the embodiment of the present invention, at least one of the second retardation layer and the third retardation layer may be a positive B plate. For example, the first retardation layer may be a layer other than the positive A plate. Also, the layer that is not a positive B plate among the second retardation layer and the third retardation layer may be a layer other than the positive A plate. Examples of the layer other than the positive A plate include a negative B plate.

[0044] Hereinafter, each member constituting the optical laminate will be described.

[0045] B. Polarizing plate B-1. Polarizer As the polarizer, any appropriate polarizer can be adopted. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0046] Specific examples of the polarizer composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and ethylene-vinyl acetate copolymer-based partially saponified films, which are subjected to a dyeing treatment with a dichroic substance such as iodine or a dichroic dye and a stretching treatment, and polyene-based alignment films such as dehydrated products of PVA and dehydrochlorinated products of polyvinyl chloride. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used because of its excellent optical properties.

[0047] The above iodine staining is performed, for example, by immersing a PVA-based film in an aqueous iodine solution. The stretching ratio of the above uniaxial stretching is preferably 3 times or more and 7 times or less. The stretching may be performed after the dyeing treatment, or may be performed while dyeing. Also, dyeing may be performed after stretching. If necessary, a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, etc. are applied to the PVA-based film. For example, by immersing the PVA-based film in water and washing it before dyeing, not only can the dirt on the surface of the PVA-based film and the anti-blocking agent be washed away, but also the PVA-based film can be swollen to prevent uneven dyeing and the like.

[0048] Specific examples of the polarizer obtained using the laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. The polarizer obtained 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 applying a PVA-based resin solution to 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 make the PVA-based resin layer a polarizer. In an embodiment of the present invention, preferably, a PVA-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Further, stretching may further include, if necessary, air stretching the laminate at a high temperature (for example, 95 °C or higher) before stretching in the aqueous boric acid solution. In addition, in an embodiment of the present invention, preferably, the laminate is subjected to a drying shrinkage treatment in which it is heated while being conveyed in the longitudinal direction to shrink by 2% or more in the width direction. Typically, the manufacturing method of the present embodiment includes sequentially performing an air-assisted stretching treatment, a dyeing treatment, a water stretching treatment, and a drying shrinkage treatment on the laminate. By introducing the auxiliary stretching, even when PVA is applied on a thermoplastic resin, it is possible to enhance the crystallinity of PVA and achieve high optical properties. At the same time, by enhancing the orientation of PVA in advance, problems such as a decrease in the orientation of PVA and dissolution when immersed in water in the subsequent dyeing process and stretching process can be prevented, and high optical properties can be achieved. Further, when the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation of polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical properties of the polarizer obtained through treatment steps such as a dyeing treatment and a water stretching treatment, which are performed by immersing the laminate in a liquid, can be improved. Furthermore, by shrinking the laminate in the width direction by the drying shrinkage treatment, the optical properties can be improved.The obtained resin substrate / polarizer laminate may be used as it is (i.e., the resin substrate may be used as the protective layer of the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate, and any appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Details of such a method for manufacturing a polarizer are described, for example, in JP-A-2012-73580 and Japanese Patent No. 6470455. The entire descriptions of these publications are incorporated herein by reference.

[0049] The thickness of the polarizer may 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 still more preferably 8 μm or less. If the thickness of the polarizer is within such a range, curling during heating can be favorably suppressed, and good appearance durability during heating can be obtained.

[0050] The polarizer preferably exhibits absorption dichroism at any wavelength in the wavelength range of 380 nm to 780 nm. The single 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 still more preferably 99.9% or more.

[0051] B-2. Protective Layer The protective layer is formed of any suitable film that can be used as a protective film for a polarizer. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based resins. Also included are thermosetting resins or ultraviolet-curing resins such as (meth)acrylic-based, urethane-based, (meth)acrylic urethane-based, epoxy-based, and silicone-based resins. In addition, glassy polymers such as siloxane-based polymers are also included. Further, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01 / 37007) can also be used. As the material of this 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. Examples include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

[0052] As described above, the optical laminate is typically disposed on the viewing side of the image display device, and the protective layer 42 is disposed on the viewing side thereof. Therefore, the protective layer may be subjected to surface treatments such as hard coat treatment, antireflection treatment, anti-sticking treatment, and antiglare treatment, as necessary. Further, the protective layer may be subjected to a treatment (typically, imparting an (elliptical) polarization function or imparting an ultra-high retardation) for improving visibility when viewing through polarized sunglasses, as necessary. By performing such a treatment, excellent visibility can be achieved even when viewing the display screen through a polarizing lens such as polarized sunglasses. Therefore, the optical laminate can also be suitably applied to an image display device that can be used outdoors.

[0053] The inner protective layer (if present) is preferably optically isotropic. As used herein, "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.

[0054] 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 even more preferably 30 μm or less. When 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).

[0055] 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 even more preferably 90% or more. Although the theoretical upper limit of the light transmittance is 100%, surface reflection occurs due to the refractive index difference between air and the retardation film, so the achievable upper limit of the light transmittance is approximately 94%.

[0056] As described above, the refractive index characteristics of the first retardation layer preferably exhibit the relationship nx > ny = nz. That is, the first retardation layer is preferably a positive A plate.

[0057] As the material for forming the first retardation layer, any suitable material can be adopted as long as the above characteristics can be obtained. Specifically, the first retardation layer may be an alignment cured layer of a liquid crystal compound (liquid crystal alignment cured layer) or a retardation film (stretched film of a polymer film).

[0058] When the first retardation layer is a liquid crystal alignment curing layer, by using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be made significantly larger than that of a non-liquid crystal material. Therefore, the thickness of the retardation layer for obtaining a desired in-plane retardation can be made significantly smaller. As a result, further thinning of the polarizing plate with a retardation layer (and as a result, the image display device) can be achieved. In this specification, the "alignment curing layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. Note that the "alignment curing layer" is a concept that includes an alignment 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 aligned in the slow axis direction of the second retardation layer (homogeneous alignment).

[0059] Examples of the liquid crystal compound include a liquid crystal compound having a nematic liquid crystal phase (nematic liquid crystal). 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 may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

[0060] When the liquid crystal compound is a liquid crystalline monomer, for example, it is preferably a polymerizable monomer and / or a crosslinkable monomer. This is because the alignment state of the liquid crystalline monomer can be fixed by polymerizing or crosslinking the liquid crystalline monomer. After aligning the liquid crystalline monomer, for example, by polymerizing or crosslinking the liquid crystalline monomers with each other, the above alignment state can be fixed. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystalline. Therefore, in the formed first retardation layer, for example, a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change peculiar to the liquid crystalline compound does not occur. As a result, the formed first retardation layer can be a retardation layer that is not affected by temperature changes and is extremely stable.

[0061] The first retardation layer may be a laminate in which a liquid crystal alignment cured layer is formed on any suitable substrate. The laminate with the 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 and laminated onto other optical functional films (such as polarizers, polarizing plates containing polarizers, etc.). 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 diacetyl cellulose and triacetyl cellulose; acrylic-based polymers; styrene-based polymers; polycarbonate, polyamide, polyimide, etc. The substrate preferably has an alignment regulating force for aligning liquid crystal molecules in a predetermined direction. The alignment regulating force can typically be imparted by rubbing alignment, stretching substrate alignment, or photo-alignment. The alignment regulating force is preferably imparted by stretching substrate alignment or photo-alignment.

[0062] 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 JP-A-2006-163343 and JP-A-2006-178389. The descriptions in these publications are incorporated herein by reference.

[0063] As described above, the first retardation layer may be a stretched film of a polymer film. Any suitable resin can be employed as the resin for forming the polymer film. Specific examples include resins that constitute positive birefringence films 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.

[0064] 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 alkylidene substitution products, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, etc., and polar group substitution products such as their halogens; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; dimethanooctahydronaphthalene, its alkyl and / or alkylidene substitution products, and polar group substitution products such as halogens, for example, 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-ethylidene-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.; trimers to tetramers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzindene, 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene. The above-mentioned norbornene-based resin may be a copolymer of a norbornene-based monomer and another monomer.

[0065] The above polycarbonate resin contains, for example, a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, di-, tri- or polyethylene glycols, and alkylene glycols or spiroglycols. The polycarbonate resin preferably contains a structural unit derived from a fluorene-based dihydroxy compound, a structural unit derived from an isosorbide-based dihydroxy compound, and a structural unit derived from spiroglycol. The polycarbonate resin may optionally contain a structural unit derived from other dihydroxy compounds. Details of the polycarbonate resin that can be preferably used in the present invention are described, for example, in JP-A Nos. 2014-10291, 2014-26266, 2015-212816, 2015-212817, and 2015-212818, and the descriptions are incorporated herein by reference.

[0066] The retardation film (stretched film) corresponding to the first retardation layer can be obtained by stretching the above polymer film under any appropriate stretching conditions. Specifically, by appropriately selecting the type of polymer, stretching conditions (e.g., stretching temperature, stretching ratio, stretching direction), and stretching method (e.g., uniaxial longitudinal stretching), a retardation film (first retardation layer) having the above desired optical properties (e.g., refractive index properties, in-plane retardation, retardation in the thickness direction) can be obtained. In particular, by adjusting the thickness (original film thickness) of the polymer film, stretching temperature, and stretching ratio, Re 1 (550) can be adjusted within the above range.

[0067] The thickness of the first retardation layer can be set so as to obtain 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.

[0068] D. The second retardation layer The range of the light transmittance of the second retardation layer at a wavelength of 550 nm is the same as the range of the light transmittance of the first retardation layer described above.

[0069] The refractive index characteristics of the second retardation layer preferably show the 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.

[0070] When the second retardation layer is a positive A plate, the configuration of the second retardation layer is as described for the first retardation layer in section C above.

[0071] When the second retardation layer is a positive B plate, the second retardation layer is preferably composed of a resin film. With such a configuration, compared with the case where the retardation layer is a liquid crystal alignment layer, lamination is easy, and the optical laminate can be excellent in mechanical strength.

[0072] 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 small. In other words, it means that the refractive index in the direction perpendicular to the stretching direction becomes large. Examples of the polymer showing negative birefringence include polymers in which a chemical bond or functional group having a large polarization anisotropy such as an aromatic ring or a carbonyl group is introduced into the side chain. Specifically, acrylic resins, styrene resins, maleimide resins, etc. can be mentioned.

[0073] The above acrylic resin can be obtained, for example, by addition-polymerizing an acrylate monomer. Examples of the acrylic resin include polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate.

[0074] The above styrene resin can be obtained, for example, by addition-polymerizing a styrene monomer. Examples of the styrene monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-dichlorostyrene, and p-t-butylstyrene.

[0075] The maleimide resin can be obtained, for example, by addition polymerization of a maleimide monomer. Examples of the maleimide monomer include 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, and N-(2-cyanophenyl)maleimide.

[0076] In the above addition polymerization, after polymerization, the birefringence characteristics of the obtained resin can also be controlled by substituting side chains, performing maleimidation or grafting reactions, and the like.

[0077] The polymer exhibiting the above negative birefringence may have other monomers copolymerized therein. By copolymerizing 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, and 1-hexene; acrylonitrile; (meth)acrylates such as methyl acrylate and methyl methacrylate; maleic anhydride; and vinyl esters such as vinyl acetate.

[0078] When the polymer exhibiting the above-mentioned negative birefringence is a copolymer of the above-mentioned styrene monomer and the above-mentioned other monomer, the blending ratio of the styrene monomer is preferably 50 mol% to 80 mol%. When the polymer exhibiting the above-mentioned negative birefringence is a copolymer of the above-mentioned maleimide monomer and the above-mentioned other monomer, the blending ratio of the maleimide monomer is preferably 2 mol% to 50 mol%. By blending in such a range, a polymer film excellent in toughness and moldability can be obtained.

[0079] As the polymer exhibiting the above-mentioned negative birefringence, preferably, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene-(meth)acrylate copolymer, styrene-maleimide copolymer, vinyl ester-maleimide copolymer, olefin-maleimide copolymer, etc. are used. These can be used alone or in combination of two or more. These polymers exhibit high negative birefringence and can be excellent in heat resistance. These polymers can be obtained, for example, from Nova Chemical Japan or Arakawa Chemical Industries, Ltd.

[0080] As the polymer exhibiting the above-mentioned negative birefringence, preferably, a polymer having a repeating unit represented by the following general formula (I) is also used. Such a polymer can exhibit even higher negative birefringence and can be excellent in heat resistance and mechanical strength. Such a polymer can be obtained, for example, by using an N-phenyl-substituted maleimide in which a phenyl group having a substituent at least in the ortho position is introduced as the N-substituent of the starting maleimide monomer.

Chemical formula

[0081] In the above general formula (I), R 1 ~R 5 each independently represents hydrogen, a halogen atom, a carboxylic acid, a carboxylic acid ester, a hydroxyl group, a nitro group, or a linear or branched alkyl group or alkoxy group having 1 to 8 carbon atoms (provided that R 1 and R5 (wherein, simultaneously, is not a hydrogen atom), R 6 and R 7 represents hydrogen or a linear or branched alkyl group or alkoxy group having 1 to 8 carbon atoms, and n represents an integer of 2 or more.

[0082] The polymer exhibiting the negative birefringence is not limited to the above, and for example, a cyclic olefin copolymer as disclosed in JP-A-2005-350544 can also be used. Further, a composition containing a polymer and inorganic fine particles as disclosed in JP-A-2005-156862, JP-A-2005-227427, etc. can also be preferably used. Further, as the polymer exhibiting the negative birefringence, one kind may be used alone, or two or more kinds may be mixed and used. Further, these can also be used after being modified by copolymerization, branching, crosslinking, molecular terminal modification (or capping), and stereoregular modification, etc.

[0083] The above polymer film may further contain any appropriate additive as necessary. 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, etc. The type and content of the additive can 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 film. When the content of the additive becomes excessively large, the transparency of the polymer film may be impaired, or the additive may ooze out from the surface of the polymer film.

[0084] As the method for forming the above-mentioned polymer film, any appropriate forming method can be adopted. For example, compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, solvent casting method, etc. can be mentioned. Among these, the extrusion molding method and the 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 a method of heating and melting a resin composition containing the above-mentioned thermoplastic resin, plasticizer, additive, etc., extruding this in a thin film shape onto the surface of a casting roll by a T-die or the like, and cooling to form a film. The solvent casting method is a method of defoaming a concentrated solution (dope) in which the resin composition is dissolved in a solvent, casting it uniformly in a thin film shape on the surface of a metallic endless belt or a rotating drum, or a plastic substrate, etc., and evaporating the solvent to form a film. Note that the molding conditions can be appropriately set according to the composition and type of the resin used, the molding process method, etc.

[0085] As the method for forming the above-mentioned polymer film, any appropriate forming method can be adopted. The molding conditions can be appropriately set according to the composition and type of the resin used, the molding process method, etc.

[0086] The retardation film (stretched film) corresponding to the second retardation layer can be obtained by stretching the above-mentioned polymer film under any appropriate stretching conditions. Specific examples of the stretching method include a uniaxial stretching method in the longitudinal direction, a uniaxial stretching method in the transverse direction, a sequential biaxial stretching method in the longitudinal and transverse directions, and a simultaneous biaxial stretching method in the longitudinal and transverse directions. Preferably, the uniaxial stretching method in the longitudinal direction, the sequential biaxial stretching method in the longitudinal and transverse directions, and the simultaneous biaxial stretching method in the longitudinal and transverse directions are used. In the polymer showing the above negative birefringence, since the refractive index in the stretching direction becomes relatively small as described above, in the case of the uniaxial stretching method in the longitudinal direction, the fast axis is in the conveying direction of the polymer film (the refractive index in the direction perpendicular 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, either the conveying direction or the width direction can be the slow axis depending on the ratio of the stretching ratios in the longitudinal and transverse directions. Specifically, when the stretching ratio in the longitudinal (conveying) direction is relatively large, the transverse (width) direction becomes the slow axis, and when the stretching ratio in the transverse (width) direction is relatively large, the longitudinal (conveying) direction becomes the slow axis.

[0087] By adjusting the thickness (original film thickness) of the polymer film, the stretching temperature, and the stretching ratio, Re of the second retardation layer 2 (550), and the Nz coefficient can be adjusted to the above ranges.

[0088] The stretching temperature (the temperature in the stretching oven when stretching the polymer film) is preferably near the glass transition temperature (Tg) of the polymer 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. If the stretching temperature is too low, there is a risk that the retardation value or the direction of the slow axis becomes non-uniform, or the polymer film crystallizes (becomes cloudy). On the other hand, if the stretching temperature is excessively high, there is a risk that the polymer film melts or the expression of the retardation is insufficient. The glass transition temperature can be determined by the DSC method according to JIS K7121-1987. Any appropriate method can be adopted for the method of controlling the temperature in the stretching oven. For example, methods using an air circulation type constant temperature oven in which hot air or cold air circulates, a heater using microwaves or far infrared rays, etc., a roll heated for temperature adjustment, a heat pipe roll, or a metal belt can be mentioned.

[0089] The stretching ratio can be set to any appropriate value according to the composition of the polymer film, the types of volatile components, etc., the residual amount of volatile components, etc., the desired retardation value, etc. For example, the feeding speed during stretching is preferably 0.5 m / min to 20 m / min from the viewpoints of the mechanical accuracy, stability, etc. of the stretching apparatus.

[0090] As described above, the method for obtaining a retardation film using a polymer showing negative birefringence has been described. However, a retardation film can also be obtained using a polymer showing positive birefringence. As a method for obtaining a retardation film using a polymer showing positive birefringence, for example, a stretching method for increasing the refractive index in the thickness direction as 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 surfaces of a film containing a polymer showing positive birefringence and performing a heat treatment can be mentioned. By shrinking the film under the action of the shrinking force of the heat-shrinkable film by heat treatment and shrinking the length direction and width direction of the film, the refractive index in the thickness direction can be increased, and a positive B plate can be obtained.

[0091] Thus, a positive B plate can be manufactured using either a polymer showing positive or negative birefringence. Generally, when using a polymer showing positive birefringence, it has an advantage in that there are many types of polymers that can be selected. When using a polymer showing negative birefringence, compared with the case of using a polymer showing positive birefringence, it has an advantage in that a retardation film excellent in the uniformity in the slow axis direction can be easily obtained due to the stretching method.

[0092] The thickness of the second retardation layer can be set so 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 still more preferably 30 μm or less.

[0093] E. Third retardation layer The range of the light transmittance of the third retardation layer at a wavelength of 550 nm is the same as the range of the light transmittance of the first retardation layer described above.

[0094] The refractive index characteristics of the third retardation layer show the relationship of nx > ny as described above, and preferably show the 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.

[0095] When the third retardation layer is a positive A plate, the third retardation layer is as described for the first retardation layer in section C above.

[0096] When the third retardation layer is a positive B plate, the third retardation layer is as described for the case where the second retardation layer is a positive B plate in section D above.

[0097] F. Image display device The optical laminate described in items A to E above can be applied to an image display device. Therefore, the 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, etc. In particular, in the image display device to which the above-described optical laminate is applied, light leakage in the diagonal direction can be reduced, so it can be suitably used for an organic EL display device. The image display device according to the embodiment of the present invention includes an image display panel and the optical laminate described in items A to E above. Typically, the image display device includes an image display panel and the optical laminate disposed on the viewing side of the image display panel.

Examples

[0098] 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.

[0099] (1) Measurement of retardation value Regarding 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 the Oji Scientific Instruments KOBRA-WPR. The measurement wavelengths were 448.1 nm, 498.7 nm, 545.6 nm, 587.4 nm, 628.8 nm, and the measurement temperature was 23°C. Also, the average refractive index was measured using an Abbe refractometer manufactured by Atago Co., Ltd., and the refractive indices nx, ny, and nz were calculated from the obtained retardation values. (2) Luminance (front luminance and diagonal luminance when displaying black) Regarding the luminance in the front direction and the diagonal direction when displaying black of the optical laminate configured in the examples and comparative examples, evaluation was performed based on simulation. The simulation used "LCDMASTER Ver.6.084" manufactured by Syntec Co., Ltd. (hereinafter sometimes referred to as the simulation device), and the extended function of the simulation device was used. Specifically, the refractive index for each wavelength of each retardation layer was converted from the data obtained in (1), and simulation data for the first retardation layer, the second retardation layer, and the third retardation layer were created. Among the axes of each retardation layer from 0° to 180° and the retardation from 30 nm to 300 nm, those with the numerical value of the front luminance and the numerical value of the diagonal luminance variation below a certain level were selected, and for each configuration, a more detailed simulation was performed. From the data obtained from the detailed simulation, the luminance in the front direction when displaying black was defined as the "front luminance". Also, for the diagonal direction, the luminance data with a polar angle of 60° and an azimuth angle from 0° to 360° were extracted, and the maximum value of the luminance in the diagonal direction was defined as the "maximum diagonal luminance", and the difference between the maximum value and the minimum value of the luminance in the diagonal direction was calculated as the "diagonal luminance variation". (3) Hue For the hues in the front direction and the diagonal direction when the image display device obtained in the examples and comparative examples was in black display, 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. For the hue in the front direction, the two-point distance of the hue from the neutral point was evaluated. For the hue in the diagonal direction, the two-point distance of the hue at a polar angle of 60° and an azimuth angle of 0° to 360° was evaluated. Based on the obtained results, the a* value and b* value for the hue in the front direction ("front hue") when in black display, and the Δa* value and Δb* value for the hue in the diagonal direction ("diagonal hue variation") were calculated, respectively.

[0100] [Production Example] (Production of Positive A Plate) <Production Examples A1 - A8> A photopolymerizable liquid crystal compound (BASF's "Paliocolor LC242" showing a nematic liquid crystal phase) was dissolved in cyclopentanone to prepare a solution with a solid content concentration of 30% by weight. To this solution, a surfactant (BIG CHEMIE's "BYK - 360") and a photopolymerization initiator (IGM Resins' "Omnirad907") were added to prepare a liquid crystalline composition solution. The addition amounts of the leveling agent and the polymerization initiator were 0.01 part by weight and 3 parts by weight, respectively, based on 100 parts by weight of the photopolymerizable liquid crystal compound. An obliquely stretched norbornene-based film (ZEON's "Zeonoa Film (ZD12)", thickness: 23 μm) was prepared, and the above liquid crystalline composition was applied onto the obliquely stretched norbornene-based film by a bar coater so that the thickness after drying was a thickness at which a desired in-plane retardation shown in Table 1 was obtained, and heated at 100°C for 3 minutes to align the liquid crystal. After cooling to room temperature, under a nitrogen atmosphere, ultraviolet rays with an integrated light amount of 400 mJ / cm 2 were irradiated to perform photocuring, and a homogeneous alignment liquid crystal layer was formed on the obliquely stretched norbornene-based film. Thereby, a retardation layer showing the characteristics of each positive A plate of Production Examples A1 - A8 was obtained.

[0101] <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. Thereafter, the mixed solution of the above-mentioned compounds was returned to room temperature, and 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-mentioned compounds, and further stirred. The solution after stirring was transparent and uniform. The obtained solution was filtered through a 0.20 μm membrane filter to obtain a polymerizable composition. Also, a polyimide solution for an alignment film was applied to a glass substrate having 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 an alignment film. The obtained coating film was subjected to a rubbing treatment using a commercially available rubbing apparatus to form an alignment film. Next, the polymerizable composition obtained above was applied to 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 obtained polymerizable composition was cooled to room temperature, using a high-pressure mercury lamp, ultraviolet rays were irradiated at an intensity of 30 mW / cm 2 for 30 seconds. Thereby, a retardation layer (thickness: 2.7 μm), which is an alignment solidification layer of a liquid crystal compound, was obtained. The in-plane retardation Re(550) of the retardation layer is as shown in Table 1. Further, Re(450) / Re(550) of the retardation layer was 0.851, showing an inverse dispersion wavelength characteristic. [Chemical formula] [Chemical formula]

[0102] (Preparation of Positive B Plate) [Production Example B1] Pellet-shaped resin of styrene-maleic anhydride copolymer (manufactured by Nova Chemical Japan Co., Ltd., trade name "Dailac D232") was extruded at 270 °C using a single-screw extruder and a T-die, and the sheet-shaped molten resin was cooled by a cooling drum to obtain a film with a thickness of 40 μm. This film (thickness: 40 μm) was longitudinally stretched freely at the free end in the conveying direction at 130 °C so that the in-plane retardation Re(550) became the value shown in Table 1 to obtain a retardation film. The retardation film thus obtained was a positive B plate showing a refractive index characteristic of nz > nx > ny. The Nz coefficient of the positive B plate is shown in Table 1.

[0103] <Production Example B2 - B3> The film before stretching (thickness: 40 μm) produced in Production Example B1 was longitudinally stretched freely at the free end in the conveying direction at 130 °C so that the in-plane retardation Re(550) and the Nz coefficient became the values shown in Table 1 to obtain a retardation film.

[0104] (Production of positive C plate) <Production Example C1 - C2> Regarding Production Examples C1 and C2, except that the retardation Rth 3 (550) was changed to 80 nm, a retardation film was obtained in the same manner as in Production Example 6 of Patent No. 6896118. The retardation film thus obtained was a positive C plate showing a refractive index characteristic of nz > nx = ny.

[0105] Note that the retardation films of the above 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 as shown in Table 1.

[0106] (Production of polarizing plate) <Production Example P1> As a thermoplastic resin substrate, an amorphous isophthalic acid copolymer polyethylene terephthalate film (thickness: 100 μm) in a long strip shape with a Tg of about 75 °C was used, and one side of the resin substrate was subjected to corona treatment. 100 parts by mass of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetylacetylated PVA (manufactured by Nippon Gohsei Chemical Industry Co., Ltd., trade name "Gosefimer") at a ratio of 9:1 was dissolved in water after adding 13 parts by mass of potassium iodide to prepare a PVA aqueous solution (coating solution). The above PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (lengthwise direction) in an oven at 130°C (air-assisted stretching treatment). Next, the laminate was immersed in an insolubilization bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 4 parts by mass of boric acid with 100 parts by mass of water) for 30 seconds (insolubilization treatment). Next, the laminate was immersed in a dyeing bath at a liquid temperature of 30°C (an aqueous iodine solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with 100 parts by mass of water) for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer becomes a desired value (dyeing treatment). Next, the laminate was immersed in a crosslinking bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with 100 parts by mass of water) for 30 seconds (crosslinking treatment). Thereafter, while the laminate was immersed in an aqueous boric acid solution at a liquid temperature of 70°C (boric acid concentration: 4 wt%, potassium iodide concentration: 5 wt%), uniaxial stretching was performed in the longitudinal direction (lengthwise direction) between rolls with different peripheral speeds so that the total stretching ratio became 5.5 times (stretching treatment in water). Thereafter, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by mass of potassium iodide with 100 parts by mass of water) (washing treatment). Thereafter, while drying in an oven maintained at about 90°C, it was brought into contact with a SUS heating roll whose surface temperature was maintained at about 75°C (dry shrinkage treatment). In this way, a polarizer with a thickness of about 5 μm was formed on the resin substrate, and a laminate having a resin substrate / polarizer structure was obtained. An HC-TAC film (thickness: 20 μm) was laminated as a protective layer on the surface of the obtained laminate on the side opposite to the resin substrate. Subsequently, the resin substrate was peeled off to obtain a polarizing plate having a configuration of HC-TAC film / polarizer.

[0107] [Example 1] A polarizing plate of Production Example P1, a retardation film of Production Example A1 as the first retardation film, a retardation film of Production Example B1 as the second retardation film, and a retardation film of Production Example A2 as the third retardation film were prepared. For each retardation film, the retardation value was measured based on the above (1). Subsequently, optical property data and refractive index data in each of the first retardation layer, the second retardation layer, and the third retardation layer were obtained based on simulation. Data for each retardation layer was created with a simulation device, and the simulation was performed three times. In the first simulation, using the extended function of the simulation device, the axes of each retardation layer were incremented by 15° within the range of 0° to 180°, and the retardation was incremented by 30 nm within the range of 30 nm to 300 nm for an exhaustive simulation. The front luminance, front hue, diagonal luminance at a polar angle of 60° at azimuth angles of 0°, 45°, 90°, and 135°, and the numerical values of the hue were extracted respectively to obtain the optimal configuration of the optical laminate in which the first retardation layer, the second retardation layer, and the third retardation layer were laminated in this order. In the second simulation, based on the optimal configuration 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° within the range of ±15° of the axis angle and an increment of 1 nm with a retardation of ±30 nm. The same data analysis as in the first simulation was performed. In the third simulation, for the laminate with the optimal value among the values obtained in the second simulation, using the simulation device, while changing the Nz coefficient of the second retardation layer, the optimization of the Nz coefficient was performed. The equal contrast curve distribution of the viewing angle at black display of the optical laminate obtained by performing the three simulations is shown in Fig. 2A.

[0108] [Example 2-3 and Comparative Example 1] Simulations were performed in the same manner as in Example 1, except that the first retardation film, the second retardation film, the third retardation film, and the angle formed by the slow axis of each retardation film and the absorption axis of the polarizer of the polarizing plate (the "angle formed by the absorption axis and the slow axis") were changed as shown in Table 1. The results are shown in Table 1. In addition, the equal contrast curve distributions of the viewing angles during black display in Examples 2 and 3 are shown in FIGS. 2B and 2C, respectively. The equal contrast curve distribution of the viewing angle during black display in Comparative Example 1 is shown in FIG. 3A.

[0109] [Comparative Example 2] Simulations were performed in the same manner as in Example 1, except that the first retardation film, the second retardation film, and the angle formed by the slow axis of each retardation film and the absorption axis of the polarizing plate (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. The results are shown in Table 1. The equal contrast curve distribution of the viewing angle during black display in Comparative Example 2 is shown in FIG. 3B.

[0110]

Table 1

[0111] [Evaluation] As is clear from the results in Table 1 and the equal contrast curve distribution diagrams of the viewing angles in FIGS. 2A to 3B, in an optical laminate including a polarizing plate including a polarizer, a first retardation layer, a second retardation layer, and a third retardation layer, at least one of the second retardation layer and the third retardation layer is a retardation layer having a refractive index characteristic showing a relationship of nz > nx > ny, so that it was found that the variation in luminance in the diagonal direction (polar angle 60°) during black display can be suppressed to a low level. That is, it was found that when at least one of the second retardation layer and the third retardation layer is a positive B plate, it can contribute to suppressing the variation in luminance in the diagonal direction during black display. As a result, when an optical laminate satisfying the above is adopted in an image display device, an image display device with suppressed light leakage in the diagonal direction can be realized.

Industrial Applicability

[0112] The optical laminate according to an embodiment of the present invention can be suitably applied to an image display device (typically, a liquid crystal display device or an organic EL display device).

Description of Reference Numerals

[0113] 10 First retardation layer 20 Second retardation layer 30 Third retardation layer 40 Polarizing plate 41 Polarizer 100 Optical laminate

Claims

1. a polarizing plate including a polarizer, a first retardation layer, a second retardation layer, and a third retardation layer in this order; At least one of the second retardation layer and the third retardation layer has a refractive index characteristic that satisfies the relationship nz>nx>ny.

2. The first retardation layer has a refractive index characteristic that satisfies the relationship of nx>ny=nz. The optical laminate according to claim 1 .

3. The second retardation layer or the third retardation layer has a refractive index characteristic that satisfies the relationship of nx>ny=nz. The optical laminate according to claim 2 .

4. The second retardation layer has a refractive index characteristic that satisfies the relationship of nz>nx>ny, The in-plane retardation Re of the first retardation layer １ (550) is 130 nm or more and 150 nm or less, The in-plane retardation Re of the second retardation layer ２ (550) is 140 nm or more and 160 nm or less, The in-plane retardation Re of the third retardation layer ３ (550) is 190 nm or more and 210 nm or less, an angle between an absorption axis of the polarizer and a slow axis of the first retardation layer is 13.5° or more and 33.5° or less; an angle between an absorption axis of the polarizer and a slow axis of the second retardation layer is −10° or more and 10° or less; the angle between the absorption axis of the polarizer and the slow axis of the third retardation layer is 62.5° or more and 82.5° or less; The optical laminate according to claim 3 .

5. The third retardation layer has a refractive index characteristic that satisfies the relationship of nz>nx>ny, The in-plane retardation Re of the first retardation layer １ (550) is equal to or greater than 185 nm and equal to or less than 205 nm; The in-plane retardation Re of the second retardation layer ２ (550) is 110 nm or more and 130 nm or less, The in-plane retardation Re of the third retardation layer ３ (550) is 50 nm or more and 70 nm or less, an angle between an absorption axis of the polarizer and a slow axis of the first retardation layer is 0° or more and 20° or less; an angle between an absorption axis of the polarizer and a slow axis of the second retardation layer is 30° or more and 50° or less; the angle between the absorption axis of the polarizer and the slow axis of the third retardation layer is 80° or more and 100° or less; The optical laminate according to claim 3 .

6. 2. The optical laminate according to claim 1, wherein the retardation layer having refractive index characteristics showing a relationship of nz>nx>ny is composed of a resin film.

7. An image display panel; The optical laminate according to any one of claims 1 to 6, Image display device.

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