WO2024080047A1

WO2024080047A1 - Optical laminate

Info

Publication number: WO2024080047A1
Application number: PCT/JP2023/032890
Authority: WO
Inventors: 卓哉田中; 章典伊▲崎▼
Original assignee: 日東電工株式会社
Priority date: 2022-10-13
Filing date: 2023-09-08
Publication date: 2024-04-18

Abstract

Provided is an optical laminate having excellent optical compensation performance in a lamination direction and an oblique direction. An optical laminate according to an embodiment of the present invention comprises: a polarizing member; and a plurality of retardation members disposed on the viewing side of the polarizing member, wherein the ellipticity measured at each of an elevation angle of 90° and an elevation angle of 30° at an azimuth angle of 0° is 0.75 or more.

Description

Optical laminate

The present invention relates to an optical laminate.

Image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices, inorganic EL display devices), are rapidly becoming popular. In image display devices, optical laminates containing polarizing members and phase difference members are widely used to realize image display and improve the performance of image display. Meanwhile, new uses of image display devices have been developed in recent years. One example of such uses is an aerial display (see, for example, Patent Document 1). Among aerial displays, aerial displays utilizing aerial imaging by retroreflection (AIRR: aerial imaging by retroreflection) are being considered for use in various situations, and there is a demand for improving the conversion efficiency from device incident light to a real image. However, even if an optical laminate containing a polarizing member and a phase difference member is applied to an AIRR-type aerial display, the optical compensation performance is insufficient, and there are cases in which light obliquely incident from a display element to the optical laminate cannot be efficiently converted. Therefore, it is difficult to create a clear aerial image.

JP 2022-31074 A

The present invention has been made to solve the above-mentioned problems of the conventional art, and its main objective is to provide an optical laminate that has excellent optical compensation performance in the stacking direction and in an oblique direction intersecting with the stacking direction.

[1] An optical laminate according to an embodiment of the present invention comprises a polarizing member and a plurality of phase difference members arranged on the viewing side of the polarizing member, and has an ellipticity of 0.75 or more measured at an azimuth angle of 0° and an elevation angle of 90° and an elevation angle of 30°.
[2] In the optical laminate according to the above [1], the ellipticity measured at an elevation angle of 90° and an elevation angle of 30° at an azimuth angle of 45° may be 0.70 or more.
[3] In the optical laminate described in [1] or [2] above, the multiple phase difference members may include, in this order from the viewing side, a first phase difference member having a refractive index of nz>nx=ny; a second phase difference member functioning as a λ/4 member; a third phase difference member having a refractive index of nz>nx≧ny; and a fourth phase difference member having a refractive index of nx>ny≧nz.
[4] In the optical laminate according to [1] or [2], the plurality of phase difference members may include, in this order from the viewing side, a first phase difference member having a refractive index of nz>nx=ny, a second phase difference member functioning as a λ/4 member, and a fifth phase difference member having a refractive index of nx>nz>ny. The angle between the absorption axis direction of the polarizing member and the slow axis direction of the fifth phase difference member may be 90°±1.5° or less.

According to an embodiment of the present invention, it is possible to realize an optical laminate that has excellent optical compensation performance in both the lamination direction and the oblique direction. If such an optical laminate is applied to a retroreflective aerial imaging device, it is possible to create a clear aerial image.

FIG. 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an optical laminate according to another embodiment of the present invention. FIG. 3 is a schematic plan view for explaining the azimuth angle in the optical laminate of FIG. FIG. 4 is a schematic side view for explaining the elevation angle in the optical laminate of FIG. FIG. 5 is a schematic diagram of an aerial imaging device including an optical stack according to one embodiment of the present invention.

Below, we will explain some representative embodiments of the present invention, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)
The definitions of terms and symbols used 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 perpendicular 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 having a wavelength of λ nm at 23° C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23° C. Re(λ) is calculated by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Retardation in the thickness direction (Rth)
"Rth(λ)" is the retardation in the thickness direction measured with light having a wavelength of λ nm at 23° C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23° C. Rth(λ) is calculated by the formula: Rth(λ)=(nx-nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz Coefficient The Nz coefficient is calculated by Nz=Rth/Re.
(5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise angles with respect to a reference direction. Thus, for example, "45°" means ±45°.

A. Overall Configuration of the Optical Laminate Figure 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention; Figure 2 is a schematic cross-sectional view of an optical laminate according to another embodiment of the present invention.
The optical laminate 100 of the illustrated example includes a polarizing member 5 including a polarizing film 51; and a plurality of phase difference members arranged on the viewing side of the polarizing member 5. In the optical laminate 100, the ellipticity measured at an elevation angle of 90° and an elevation angle of 30° at an azimuth angle of 0° is 0.75 or more. The ellipticity measured at an elevation angle of 90° at an azimuth angle of 0° is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.88 or more, and particularly preferably 0.90 or more. The ellipticity measured at an elevation angle of 30° at an azimuth angle of 0° is preferably 0.80 or more, more preferably 0.82 or more, even more preferably 0.84 or more, and particularly preferably 0.85 or more.
When the ellipticity measured at an azimuth angle of 0° and an elevation angle of 90° and an elevation angle of 30° is equal to or greater than the lower limit, the optical compensation performance can be improved in the stacking direction of the optical laminate and in the oblique direction intersecting the stacking direction. Therefore, when such an optical laminate is applied to an aerial imaging device described later, light incident in an oblique direction on the optical laminate can be efficiently converted, and a clear aerial image can be created. The upper limit of the ellipticity measured at an azimuth angle of 0° and an elevation angle of 90° and an elevation angle of 30° is typically 1.00 or less, and is, for example, 0.95 or less.

In this specification, the term "azimuth angle" refers to the angle θ1 between the absorption axis direction of the polarizing film as a reference and the surface direction of the optical laminate (direction perpendicular to the lamination direction) as shown in Fig. 3. When the azimuth angle θ1 is 0°, the surface direction and the reference direction are substantially parallel to each other.
In this specification, the "elevation angle" is the angle θ2 between the reference direction and the measurement direction located on the same virtual plane as the reference direction, as shown in FIG. 4, based on the surface direction of the optical laminate. The measurement direction is typically a direction connecting the light receiving part of an ellipticity measuring device (typically a Mueller matrix polarimeter) and any point on the surface of the optical laminate when measuring the ellipticity. When the elevation angle is 0°, the measurement direction and the reference direction are substantially parallel, and when the elevation angle is 90°, the measurement direction and the stacking direction are substantially parallel.
In this specification, "ellipticity" is an index showing whether light (polarized light) is close to circularly polarized light or close to linearly polarized light, and is the ratio (b/a) of the minor axis radius b to the major axis radius a of elliptically polarized light. An ellipticity of 1.0 means substantially circularly polarized light, and an ellipticity of 0 means substantially linearly polarized light.
The ellipticity can be calculated, for example, by the following method.
Light having wavelengths of 450 nm, 550 nm, and 650 nm is incident on the optical laminate from the polarizing member side, and the major axis radius a and the minor axis radius b of the emitted light (elliptically polarized light) that passes through multiple phase difference members are measured at a predetermined elevation angle and azimuth angle, and the average value of the minor axis radius b/major axis radius a of the lights having different wavelengths is defined as the ellipticity. More specifically, the ellipticity can be calculated in accordance with the method described in the examples below.

In one embodiment, the optical laminate 100 has an ellipticity of 0.70 or more measured at an elevation angle of 90° and an elevation angle of 30° at an azimuth angle of 45°. The ellipticity measured at an elevation angle of 90° at an azimuth angle of 45° is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.88 or more, and particularly preferably 0.90 or more. The ellipticity measured at an elevation angle of 30° at an azimuth angle of 45° is preferably 0.80 or more, more preferably 0.81 or more, even more preferably 0.83 or more, and particularly preferably 0.84 or more.
When the ellipticity measured at an elevation angle of 90° and an elevation angle of 30° at an azimuth angle of 45° is equal to or greater than the lower limit, the optical compensation performance in the stacking direction and in the oblique direction can be stably improved. The upper limit of the ellipticity measured at an elevation angle of 90° and an elevation angle of 30° at an azimuth angle of 45° is typically 1.00 or less, and is, for example, 0.95 or less.

As shown in Figures 1 and 2, the multiple phase difference members typically include, in this order from the viewing side, a first phase difference member 1 having a refractive index of nz>nx=ny; and a second phase difference member 2 functioning as a λ/4 member. With this configuration, the optical compensation performance in the stacking direction and oblique directions can be improved more stably.

As shown in FIG. 1 , in one embodiment, the multiple phase difference members include, in this order from the viewing side, the first phase difference member 1 described above; the second phase difference member 2 described above; a third phase difference member 3 having a refractive index of nz>nx≧ny; and a fourth phase difference member 4 having a refractive index of nx>ny≧nz.
2, the plurality of phase difference members may include the first phase difference member 1 described above; the second phase difference member 2 described above; and a fifth phase difference member 50 having a refractive index of nx>nz>ny, in this order from the viewing side. That is, the plurality of phase difference members may include the fifth phase difference member 50 instead of the third phase difference member 3 and the fourth phase difference member 4. In this case, the angle between the absorption axis direction of the polarizing film 51 provided in the polarizing member 5 and the slow axis direction of the fifth phase difference member 50 is, for example, 90°±1.5° or less (i.e., 88.5° or more and 91.5° or less), preferably less than 90°±1.0° (i.e., more than 89.0° and less than 91.0°), and more preferably 90°±0.5° or less (i.e., 89.5° or more and 90.5° or less).
According to these configurations, the optical compensation performance in the stacking direction and in the oblique direction can be improved more stably.
In addition, the number of phase difference members is four in Fig. 1 and three in Fig. 2, but the number of phase difference members is not limited to this. The multiple phase difference members may further include another phase difference member in addition to the above-mentioned phase difference members.

In one embodiment, the optical laminate 100 further comprises a substrate 6 located on the opposite side of the first phase difference member 1 from the second phase difference member 2; and an optical functional layer 7 located on the opposite side of the first phase difference member 1 from the substrate 6. By providing the optical laminate with an optical functional layer, it is possible to impart an optical function corresponding to the optical functional layer to the optical laminate.

In one embodiment, the optical laminate 100 further includes a first surface protective film 8 located on the opposite side of the first phase difference member 1 from the second phase difference member 2. In the illustrated example, the first surface protective film 8 is located on the opposite side of the substrate 6 from the first phase difference member 1.

The optical laminate 100 may further include a second surface protective film 9. The second surface protective film 9 is located on the opposite side of the first phase difference member 1 with respect to the first surface protective film 8, and is temporarily attached to the first surface protective film 8.

In one embodiment, the optical laminate 100 further includes an adhesive layer 20 located on the opposite side of the polarizing member 5 to the multiple retardation members (opposite the viewing side). This allows the optical laminate 100 to be attached to various optical components (e.g., image display cells, retroreflective sheets) by the adhesive layer 20.

The optical laminate 100 may further include a release liner 10. The release liner 10 is located on the opposite side of the adhesive layer 20 from the polarizing member 5, and is temporarily attached to the surface of the adhesive layer 20. The release liner 10 is temporarily attached to the adhesive layer 20 until the optical laminate is attached to an optical component, and is peeled off from the adhesive layer 20 when the optical laminate is attached.

The optical laminate 100 is typically rectangular when viewed from the stacking direction. More specifically, the optical laminate 100 may be rectangular with long sides of about 10 mm to 70 mm and short sides of about 10 mm to 70 mm, or long sides of about 20 mm to 40 mm and short sides of about 10 mm to 30 mm, and more specifically, long sides of about 30 mm and short sides of about 20 mm.

The components of the optical laminate are explained below.

B. Polarizing Member The polarizing member 5 is typically an absorptive polarizing member. The polarizing member 5 includes a polarizing film 51. The polarizing member 5 may further include a protective layer. The protective layer may be provided on at least one surface of the polarizing film, or may be provided on both surfaces of the polarizing film. In the illustrated example, the polarizing member 5 includes a protective layer 52 provided on the surface of the polarizing film 51 opposite to the viewing side. The protective layer 52 is typically bonded to the polarizing film 51 via any suitable adhesive layer 53. A typical example of the adhesive forming the adhesive layer 53 is an ultraviolet-curing adhesive. The thickness of the adhesive layer 53 is, for example, 1.5 μm or more, preferably 2.0 μm or more, and, for example, 5.0 μm or less, preferably 3.0 μm or less.

B-1. Polarizing film Any appropriate absorptive polarizing film may be adopted as the polarizing film 51. The polarizing film 51 typically includes a resin film containing a dichroic material. The polarizing film 51 may be made of a single-layer resin film or may be made using a laminate of two or more layers.

When made from a single-layer resin film, for example, an absorptive polarizing film can be obtained by subjecting a hydrophilic polymer film such as a polyvinyl alcohol (PVA)-based film, a partially formalized PVA-based film, or an ethylene-vinyl acetate copolymer-based partially saponified film to a dyeing process using a dichroic substance such as iodine or a dichroic dye, and a stretching process. Among these, an absorptive polarizing film obtained by dyeing a PVA-based film with iodine and stretching it uniaxially is preferred.

The dyeing with iodine is carried out, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing process, or may be carried out while dyeing. Alternatively, the film may be stretched and then dyed. If necessary, the PVA-based film may be subjected to a swelling process, a crosslinking process, a washing process, a drying process, etc.

When the laminate is produced using the above-mentioned two or more layer laminate, examples of 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 laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. The absorptive polarizing film 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 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; and stretching and dyeing the laminate to make the PVA-based resin layer into an absorptive polarizing film. In this embodiment, preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. The stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, the stretching may further include air-stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the boric acid aqueous solution, if necessary. In addition, in this embodiment, the laminate is preferably subjected to a drying shrinkage treatment in which the laminate is heated while being conveyed in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing the auxiliary stretching, it is possible to increase the crystallinity of PVA even when PVA is applied onto a thermoplastic resin, and it is possible to achieve high optical properties. At the same time, by increasing the orientation of PVA in advance, problems such as a decrease in the orientation of PVA or dissolution can be prevented when the PVA is immersed in water in the subsequent dyeing step or stretching step, and it is possible to achieve high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of the absorptive polarizing film obtained by immersing the laminate in a liquid in a treatment process such as a dyeing process and an underwater stretching process. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction by a drying shrinkage process. The obtained resin substrate/absorptive polarizing film laminate may be used as it is (i.e., the resin substrate may be used as a protective layer for the absorptive polarizing film), or any suitable protective layer may be laminated on the peeled surface obtained by peeling the resin substrate from the resin substrate/absorptive polarizing film laminate, or on the surface opposite to the peeled surface. Details of the manufacturing method of such an absorptive polarizing film are described in, for example, JP 2012-73580 A and JP 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

The thickness of the polarizing film is, for example, 1 μm or more and 20 μm or less, preferably 2 μm or more and 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, particularly preferably 8 μm or less, and especially preferably 5 μm or less.

The polarizing film preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The crossed transmittance (Tc) of the polarizing film is, for example, 0.5% or less, preferably 0.1% or less, and more preferably 0.05% or less. The single transmittance (Ts) of the polarizing film is, for example, 41.0% to 46.0%, and preferably 42.0% or more. The degree of polarization of the polarizing film is, for example, 97.0 to 99.997% or more, preferably 99.0% or more, and more preferably 99.9% or more.

B-2. Protective layer The protective layer is formed of any suitable film that can be used as a protective layer for a polarizing film. Specific examples of materials that are the main components of the film include cycloolefin (COP) resins such as polynorbornene resins, polyester resins such as polyethylene terephthalate (PET) resins, cellulose resins such as triacetyl cellulose (TAC), transparent resins such as polycarbonate (PC), (meth)acrylic resins, polyvinyl alcohol resins, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polyolefins, and acetate resins. In addition, thermosetting resins or ultraviolet-curing resins such as (meth)acrylic resins, urethane resins, (meth)acrylic urethane resins, epoxy resins, and silicone resins are also included. Note that the term "(meth)acrylic resin" refers to acrylic resins and/or methacrylic resins. In addition, glassy polymers such as siloxane polymers are also included. Also usable is the polymer film described in JP 2001-343529 A (WO 01/37007). 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, for example, a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above resin composition. The materials of the resin film can be used alone or in combination.

The thickness of the protective layer is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm.

In addition, a hard coat layer 54 may be provided on the surface of the protective layer 52 opposite to the polarizing film 51 (opposite to the viewing side). That is, the polarizing member 5 may include a hard coat layer 54. The hard coat layer 54 is formed directly on the surface of the protective layer 52. In this specification, "directly" means that no adhesive layer (adhesive layer or pressure-sensitive adhesive layer) is interposed.
The hard coat layer 54 preferably has sufficient surface hardness, excellent mechanical strength, and excellent light transmittance. The hard coat layer 54 may be formed from any appropriate resin. The hard coat layer 54 is typically formed from an ultraviolet curing resin. Examples of ultraviolet curing resins include polyester, acrylic, urethane, amide, silicone, and epoxy resins. The thickness of the hard coat layer 54 is, for example, 0.5 μm or more, preferably 1 μm or more, for example, 20 μm or less, and preferably 15 μm or less.

C. First Phase Difference Member The first phase difference member 1 is located on the opposite side of the polarizing member 5 with respect to the second phase difference member 2. The first phase difference member 1 is typically a phase difference film. The first phase difference member 1 is typically attached to the second phase difference member 2 via any suitable adhesive layer 11. A typical example of the adhesive forming the adhesive layer 11 is an ultraviolet-curing adhesive. The thickness of the adhesive layer 11 is, for example, 1.5 μm or more, preferably 2.0 μm or more, and, for example, 5.0 μm or less, preferably 3.0 μm or less.

The first phase difference member 1 has a refractive index of nz>nx=ny as described above. A layer (film) having a refractive index of nz>nx=ny may be called a "positive C plate" or the like. Note that "nx=ny" includes not only the case where nx and ny are completely equal, but also the case where they are substantially equal. The in-plane retardation Re(550) of the first phase difference member 1 may be, for example, 0 nm or more and less than 10 nm.
The thickness direction retardation Rth(550) of the first retardation member 1 is typically less than 0 nm, preferably −5 nm or less, more preferably −50 nm or less, and for example, −200 nm or more, preferably −150 nm or more, more preferably −110 nm or more.

The first phase difference member 1 may be formed of any appropriate material. The first phase difference member 1 is preferably composed of a film containing a liquid crystal material fixed in homeotropic alignment. The liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method of forming the optical compensation layer include the liquid crystal compound and the method of forming the optical compensation layer described in [0020] to [0028] of JP-A-2002-333642. In this case, the thickness of the first phase difference member 1 is, for example, 10 μm or less, preferably 8 μm or less, more preferably 5 μm or less, and typically 0.5 μm or more.

D. Second Phase Difference Member The second phase difference member 2 is located between the first phase difference member 1 and the third phase difference member 3 in FIG. 1, and between the first phase difference member 1 and the fifth phase difference member 50 in FIG. 2. The second phase difference member 2 is typically a phase difference film. The second phase difference member 2 is typically attached to the third phase difference member 3 or the fifth phase difference member 50 via any suitable adhesive layer 21. Examples of adhesives that form the adhesive layer 21 include (meth)acrylic adhesives, urethane adhesives, silicone adhesives, and rubber adhesives, and preferably (meth)acrylic adhesives. The thickness of the adhesive layer 21 is, for example, 3.5 μm or more and 35 μm or less.

The second phase difference member 2 functions as a λ/4 member as described above. The second phase difference member 2 typically has a refractive index of nx>ny≧nz. Note that "ny=nz" here includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal.
The in-plane retardation Re(550) of the second phase difference member 2 is typically 100 nm or more and 200 nm or less, preferably 110 nm or more and 180 nm or less, more preferably 130 nm or more and 150 nm or less. The Nz coefficient of the second phase difference member 2 is preferably 0.9 to 2.0, more preferably 0.9 to 1.5, and further preferably 0.9 to 1.2.

The angle between the absorption axis direction of the polarizing film 51 and the slow axis direction of the second phase difference member 2 is typically 40° or more and 50° or less, preferably 42° or more and 48° or less, more preferably 44° or more and 46° or less, and particularly preferably 45°.
The second phase difference member 2 may exhibit an inverse dispersion wavelength characteristic in which the phase difference value increases according to the wavelength of the measurement light, may exhibit a positive wavelength dispersion characteristic in which the phase difference value decreases according to the wavelength of the measurement light, or may exhibit a flat wavelength dispersion characteristic in which the phase difference value hardly changes depending on the wavelength of the measurement light. The second phase difference member 2 preferably exhibits an inverse dispersion wavelength characteristic. That is, the second phase difference member 2 preferably satisfies the relationship Re(450)<Re(550).

The resin constituting the second phase difference member 2 may be, for example, a polycarbonate-based resin, a polyester carbonate-based resin, a polyester-based resin, a polyvinyl acetal-based resin, a polyarylate-based resin, a cyclic olefin-based resin, a cellulose-based resin, a polyvinyl alcohol-based resin, a polyamide-based resin, a polyimide-based resin, a polyether-based resin, a polystyrene-based resin, or a (meth)acrylic-based resin. Such resins may be used alone or in combination. The resin constituting the second phase difference member 2 preferably includes a polycarbonate-based resin.

The polycarbonate-based resin preferably contains at least one structural unit selected from the group consisting of structural units represented by the following general formula (1) and/or structural units represented by the following general formula (2). These structural units are structural units derived from divalent oligofluorene, and may be referred to as oligofluorene structural units hereinafter. Such polycarbonate-based resins and the like have positive refractive index anisotropy.

In general formulas (1) and (2), R ¹ to R ³ are each independently a direct bond or a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms; R ⁴ to R ⁹ are each independently a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted aryl group having 4 to 10 carbon atoms, a substituted or unsubstituted acyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted aryloxy group having 1 to 10 carbon atoms, a substituted or unsubstituted amino group, a substituted or unsubstituted vinyl group having 1 to 10 carbon atoms, a substituted or unsubstituted ethynyl group having 1 to 10 carbon atoms, a sulfur atom having a substituent, a silicon atom having a substituent, a halogen atom, a nitro group, or a cyano group; provided that R ⁴ to R ⁹ may be the same or different, and at least two adjacent groups among R ⁴ to R ⁹ may be bonded to each other to form a ring.

The content of the oligofluorene structural unit in the polycarbonate resin is, for example, 1 mass% or more, preferably 10 mass% or more, more preferably 15 mass% or more, and even more preferably 18 mass% or more, and is, for example, 40 mass% or less, preferably 35 mass% or less, more preferably 30 mass% or less, and even more preferably 25 mass% or less. When the content of the oligofluorene structural unit is equal to or greater than the above lower limit, the desired reverse dispersion wavelength dependency can be stably expressed in the second phase difference member. When the content of the oligofluorene structural unit is equal to or less than the above upper limit, the phase difference can be stably expressed.

More preferably, the polycarbonate-based resin contains, in addition to the oligofluorene structural unit, a structural unit represented by the following structural formula (3) and/or a structural unit represented by the following structural formula (4). When the polycarbonate-based resin contains the structural unit represented by the following structural formula (3) and/or the following structural formula (4), the second phase difference member 2 can exhibit the desired reverse dispersion wavelength dependency more stably.

The content ratio of the structural unit represented by the above structural formula (3) in the polycarbonate-based resin is, for example, 5 mass% or more, preferably 10 mass% or more, more preferably 20 mass% or more, and even more preferably 25 mass% or more, and is, for example, 90 mass% or less, preferably 70 mass% or less, and more preferably 50 mass% or less.
The content ratio of the structural unit represented by the above structural formula (4) in the polycarbonate-based resin is, for example, 5 mass% or more, preferably 10 mass% or more, and more preferably 15 mass% or more, and for example, 90 mass% or less, preferably 70 mass% or less, and more preferably 50 mass% or less.

The resin constituting the second phase difference member 2 particularly preferably contains a (meth)acrylic resin in addition to a polycarbonate resin.
The (meth)acrylic resin typically contains a structural unit derived from methyl methacrylate. The content ratio of the structural unit derived from methyl methacrylate in the (meth)acrylic resin is, for example, 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. If the content ratio of the structural unit derived from methyl methacrylate is equal to or more than the above lower limit, excellent compatibility with the polycarbonate resin can be exhibited. The content ratio of the structural unit derived from methyl methacrylate is typically 100% by mass or less.
The weight average molecular weight Mw of the (meth)acrylic resin is, for example, 10,000 or more, preferably 30,000 or more, more preferably 50,000 or more, and is, for example, 200,000 or less, preferably 180,000 or less, more preferably 150,000 or less. The weight average molecular weight is a polystyrene-equivalent molecular weight measured by GPC. If the weight average molecular weight Mw is within this range, excellent compatibility with the polycarbonate resin can be stably expressed.
The content of the (meth)acrylic resin in the resin constituting the second phase difference member 2 is, for example, 0 mass% or more, preferably 0.5 mass% or more, more preferably 0.6 mass% or more, and for example, 2.0 mass% or less, preferably 1.5 mass% or less, more preferably 1.0 mass% or less, even more preferably 0.9 mass% or less, and particularly preferably 0.8 mass% or less. When the content of the (meth)acrylic resin is within the above range, the extensibility and retardation expression can be significantly increased, and haze can be suppressed.

Such a second retardation member 2 is typically a stretched film of a polymer film formed from the resin constituting the above-mentioned second retardation member, and is prepared by stretching a polymer film.
The thickness of the second phase difference member 2 can be set so as to obtain desired optical characteristics. The thickness of the second phase difference member 2 is, for example, 15 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and is, for example, 60 μm or less, preferably 55 μm or less, and further preferably 50 μm or less.

E. Third Phase Difference Member As shown in Fig. 1, the third phase difference member 3 is located between the second phase difference member 2 and the fourth phase difference member 4. The third phase difference member 3 is typically attached to the fourth phase difference member 4 via any appropriate adhesive layer 31. The adhesive forming the adhesive layer 31 and the range of the thickness of the adhesive layer 31 are similar to those of the adhesive layer 11 described above.

As described above, the third phase difference member 3 has a refractive index of nz>nx≧ny. The third phase difference member 3 preferably has a refractive index of nz>nx>ny. A layer (film) having a refractive index of nz>nx>ny is sometimes called a "positive B plate" or the like.
The in-plane retardation Re(550) of the third retardation member 3 is, for example, 15 nm or more, preferably 20 nm or more, and is, for example, 55 nm or less, preferably 45 nm or less.
The third retardation member 3 has a thickness direction retardation Rth(550) of typically 0 nm or less, preferably −20 nm or less, more preferably −60 nm or less, for example, −250 nm or more, preferably −200 nm or more, more preferably −150 nm or more.

When the third phase difference member 3 has a refractive index of nz>nx>ny, the angle between the slow axis direction of the third phase difference member 3 and the absorption axis direction of the polarizing film 51 is typically 80° to 100°, preferably 85° to 95°, more preferably 88° to 92°, and even more preferably 89° to 91°. The slow axis direction of the third phase difference member 3 and the absorption axis direction of the polarizing film 51 may be substantially parallel. In this case, the angle between the slow axis direction of the third phase difference member 3 and the absorption axis direction of the polarizing film 51 is typically 0°±5° or less, and preferably 0°±1° or less.

The third phase difference member 3 may exhibit a reverse dispersion wavelength characteristic, a positive wavelength dispersion characteristic, or a flat wavelength dispersion characteristic. The third phase difference member 3 preferably exhibits a reverse dispersion wavelength characteristic. That is, the third phase difference member 3 preferably satisfies the relationship Re(450)<Re(550).

The third phase difference member 3 may have any appropriate configuration. Specifically, it may be a single phase difference member, or may be a laminate of two or more identical or different phase difference members. The third phase difference member 3 is preferably a single phase difference member (phase difference film).
Examples of the resin constituting the third phase difference member 3 include thermoplastic resins, and preferably, polymers exhibiting negative birefringence and polymers exhibiting positive birefringence. Such resins can be used alone or in combination. More preferably, the resin constituting the third phase difference member 3 includes a polymer exhibiting negative birefringence. By using a polymer exhibiting negative birefringence, a phase difference member having an index ellipsoid of nz>nx>ny and excellent uniformity in the slow axis direction can be easily obtained. Here, "exhibiting negative birefringence" means that when a polymer is oriented by stretching or the like, the refractive index in the stretching direction becomes relatively small. In other words, the refractive index in the direction perpendicular to the stretching direction becomes large. Examples of polymers exhibiting negative birefringence include polymers in which a chemical bond or functional group with large polarization anisotropy, such as an aromatic ring or a carbonyl group, is introduced into the side chain. Specifically, examples include acrylic resins, styrene resins, maleimide resins, and fumaric acid ester resins, and preferably styrene resins and fumaric acid ester resins.
Preferred examples of the styrene-based resin constituting the third phase difference member 3 include styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, styrene-(meth)acrylate copolymer, styrene-maleimide copolymer, vinyl ester-maleimide copolymer, and olefin-maleimide copolymer.
As the fumaric acid ester-based resin constituting the third phase difference member 3, a fumaric acid ester-(meth)acrylate copolymer is preferably used.
These can be used alone or in combination of two or more.

As the polymer exhibiting negative birefringence, a polymer having a repeating unit represented by the following general formula (I) is preferably used. Such a polymer exhibits even higher negative birefringence and can have excellent 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 at the ortho position is introduced as the N-substituent of the maleimide monomer as the starting material.

In the above general formula (I), R ₁ to R ₅ each independently represent hydrogen, a halogen atom, a carboxylic acid, a carboxylate, a hydroxyl group, a nitro group, or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms (provided that 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 greater.

Such a third phase difference member 3 is typically a stretched film of a polymer film formed from the resin constituting the third phase difference member 3 described above, and is prepared by stretching the polymer film under any appropriate stretching conditions.
The thickness of the third phase difference member 3 can be set so as to obtain desired optical characteristics. The thickness of the third phase difference member 3 is, for example, 5 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and is, for example, 70 μm or less, preferably 60 μm or less, and further preferably 40 μm or less.

F. Fourth phase difference member 4
The fourth phase difference member 4 is typically attached to the polarizing film 51 via any appropriate adhesive layer 41. The adhesive forming the adhesive layer 41 and the range of the thickness of the adhesive layer 41 are similar to those of the above-mentioned adhesive layer 11. The fourth phase difference member 4 is typically a phase difference film.

The fourth phase difference member 4 exhibits a refractive index of nx>ny≧nz as described above. A layer (film) having a refractive index of nx>ny>nz may be called a "negative B plate" or the like. A layer (film) having a refractive index of nx>ny=nz may be called a "positive A plate" or the like. Note that "ny=nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. The fourth phase difference member 4 preferably exhibits a refractive index of nx>ny>nz.
The in-plane retardation Re(550) of the fourth retardation member 4 is, for example, 70 nm or more, preferably 90 nm or more, and is, for example, 140 nm or less, preferably 130 nm or less.
The fourth retardation member 4 has a thickness direction retardation Rth(550) of, for example, 40 nm or more, preferably 60 nm or more, and for example, 120 nm or less, preferably 100 nm or less.

The angle between the slow axis direction of the fourth phase difference member 4 and the absorption axis direction of the polarizing film 51 is typically 80° to 100°, preferably 85° to 95°, more preferably 88° to 92°, and even more preferably 89° to 91°. The slow axis direction of the fourth phase difference member 4 and the absorption axis direction of the polarizing film 51 may be substantially parallel. In this case, the angle between the slow axis direction of the fourth phase difference member 4 and the absorption axis direction of the polarizing film 51 is typically 0°±5° or less, and preferably 0°±1° or less.
The slow axis direction of the third phase difference member 3 is preferably substantially parallel to the slow axis direction of the fourth phase difference member 4. In this case, the angle formed between the slow axis direction of the third phase difference member 3 and the slow axis direction of the fourth phase difference member 4 is typically 0°±5° or less, preferably 0°±1° or less.

The fourth phase difference member 4 may exhibit a reverse wavelength dispersion characteristic, a positive wavelength dispersion characteristic, or a flat wavelength dispersion characteristic. The fourth phase difference member 4 preferably exhibits a flat wavelength dispersion characteristic.

The resin constituting the fourth phase difference member 4 may be, for example, a norbornene-based resin, a polycarbonate-based resin, a cellulose-based resin, a polyvinyl alcohol-based resin, or a polysulfone-based resin. Such resins may be used alone or in combination. The resin constituting the fourth phase difference member 4 preferably includes a norbornene-based resin and/or a cellulose-based resin.

Such a fourth phase difference member 4 is typically a stretched film of a polymer film formed from the resin constituting the fourth phase difference member 4 described above, and is prepared by stretching the polymer film under any appropriate stretching conditions.
The thickness of the fourth phase difference member 4 can be set so as to obtain desired optical characteristics. The thickness of the fourth phase difference member 4 is, for example, 10 μm or more, preferably 20 μm or more, more preferably 60 μm or more, and is, for example, 100 μm or less, preferably 90 μm or less, and further preferably 80 μm or less.

G. Fifth Retardation Member As shown in FIG. 2, the fifth retardation member 50 is typically attached to a polarizing film 51 via any suitable adhesive layer 41 .

As described above, the fifth phase difference member 50 has a refractive index of nx>nz>ny. A layer (film) having a refractive index of nx>nz>ny is sometimes called a "Z film" or the like.
The in-plane retardation Re(550) of the fifth retardation member 50 is typically 210 nm or more and 360 nm or less, and preferably 250 nm or more and 290 nm or less.
The Nz coefficient of the fifth phase difference member 50 is typically 0.1 or more and 1.0 or less, and preferably 0.3 or more and 0.7 or less.

The fifth phase difference member 50 may exhibit a reverse wavelength dispersion characteristic, a positive wavelength dispersion characteristic, or a flat wavelength dispersion characteristic. The fifth phase difference member 50 preferably exhibits a flat wavelength dispersion characteristic.

The fifth phase difference member 50 is typically a phase difference film made of any suitable resin that can realize the above characteristics. Examples of the resin that constitutes the fifth phase difference member 50 include polyarylate resins, polyamide resins, polyimide resins, polyester resins, polyaryletherketone resins, polyamideimide resins, polyesterimide resins, polyvinyl alcohol resins, polyfumaric acid ester resins, polyethersulfone resins, polysulfone resins, cycloolefin resins, polycarbonate resins, cellulose resins, and polyurethane resins. These resins can be used alone or in combination.
As the resin constituting the fifth phase difference member 50, a cycloolefin resin is preferably used, and more preferably a norbornene resin is used. Specific examples of the norbornene resin include "cycloolefin resin obtained by hydrogenating a ring-opening polymer of a norbornene monomer" described in JP-A-2006-208925.

The fifth phase difference member 50 can be produced, for example, by laminating a high shrinkage film (e.g., a polypropylene film) to both sides of a polymer film mainly composed of the above-mentioned resin, and then heat-stretching the film by a longitudinal uniaxial stretching method using a roll stretching machine. The high shrinkage film is used to impart a shrinkage force in a direction perpendicular to the stretching direction during heat stretching, and to increase the refractive index (nz) in the thickness direction of the fifth phase difference member 50. There are no particular limitations on the method of laminating the high shrinkage film to both sides of the polymer film, but examples of the method include a method of providing an acrylic adhesive layer having an acrylic polymer as a base polymer between the polymer film and the high shrinkage film to bond them together.
The thickness of the fifth phase difference member 50 is typically 20 μm or more, preferably 30 μm or more, and more preferably 40 μm or more, and is typically 200 μm or less, and preferably 150 μm or less.

H. Substrate The substrate 6 is a substrate for forming a functional layer for forming the optical functional layer 7, and is located on the opposite side (visualization side) of the second phase difference member 2 with respect to the first phase difference member 1. The substrate 6 is typically attached to the first phase difference member 1 via any appropriate pressure-sensitive adhesive layer 61. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer 61 and the thickness range of the pressure-sensitive adhesive layer 61 are the same as those of the pressure-sensitive adhesive layer 21 described above.

The substrate 6 is formed of any suitable resin film. Examples of resins constituting the resin film include polyester-based resins such as polyethylene terephthalate (PET), cycloolefin-based resins such as norbornene-based resins, resins (COC) obtained by addition polymerization of cycloolefins (e.g., norbornene) and α-olefins (e.g., ethylene), cellulose-based resins such as triacetyl cellulose (TAC), and (meth)acrylic resins. Such resins can be used alone or in combination. The resin constituting the substrate 6 preferably contains a (meth)acrylic resin, and more preferably contains a (meth)acrylic resin having a glutarimide structure.

The thickness of the substrate 6 can be appropriately set depending on the purpose. The thickness of the substrate 6 is, for example, 20 μm or more, preferably 50 μm or more, more preferably 70 μm or more, and is, for example, 200 μm or less, preferably 150 μm or less, more preferably 90 μm or less.

I. Optical Functional Layer The optical functional layer 7 is typically formed directly on the surface (viewing side surface) of the substrate 6 opposite to the first phase difference member 1. Examples of the optical functional layer 7 include a hard coat layer, an anti-reflection layer, an anti-sticking layer, and an anti-glare layer. In the illustrated example, the optical functional layer 7 is an anti-reflection layer 7a.

The anti-reflection layer 7a is provided to prevent reflection of external light (eg, fluorescent light) and the like.
The antireflection layer 7a may have any suitable structure. Representative structures of the antireflection layer 7a include (1) a single layer of a low refractive index layer having an optical thickness of 120 nm to 140 nm and a refractive index of about 1.35 to 1.55, (2) a laminate having a medium refractive index layer, a high refractive index layer, and a low refractive index layer in this order from the substrate 6, and (3) an alternating multilayer laminate of a high refractive index layer and a low refractive index layer.

Examples of materials that can form a low refractive index layer include silicon oxide (SiO ₂ ) and magnesium fluoride (MgF ₂ ). The refractive index of the low refractive index layer is typically about 1.35 to 1.55. Examples of materials that can form a high refractive index layer include titanium oxide (TiO ₂ ), niobium oxide (Nb ₂ O ₃ or Nb ₂ O ₅ ), tin-doped indium oxide (ITO), antimony-doped tin oxide (ATO), and ZrO ₂ -TiO _2. The refractive index of the high refractive index layer is typically about 1.60 to 2.20. Examples of materials that can form a medium refractive index layer include titanium oxide (TiO ₂ ) and a mixture of a material that can form a low refractive index layer and a material that can form a high refractive index layer (for example, a mixture of titanium oxide and silicon oxide). The refractive index of the medium refractive index layer is typically about 1.50 to 1.85. The thicknesses of the low refractive index layer, the medium refractive index layer and the high refractive index layer can be set so as to realize an appropriate optical film thickness depending on the layer structure of the antireflection layer, the desired antireflection performance, and the like.

The antireflection layer 7a has a thickness of, for example, about 20 nm to 300 nm.
The difference between the maximum reflectance and the minimum reflectance of the antireflection layer 7a in the wavelength range of 400 nm to 700 nm is preferably 2.0% or less, more preferably 1.9% or less, and even more preferably 1.8% or less. If the difference between the maximum reflectance and the minimum reflectance is in such a range, coloring of reflected light can be effectively prevented.

J. First Surface Protective Film In the illustrated example, the first surface protective film 8 is located on the opposite side (visualization side) of the first phase difference member 1 with respect to the substrate 6, and is attached to the optical functional layer 7 (more specifically, the antireflection layer 7a) by an adhesive layer 82. The first surface protective film 8 may be temporarily attached during the transportation process of the optical laminate and peeled off before use of the optical laminate (used as a processing material), or may be used while still attached to the surface of the optical laminate (for the purpose of permanent adhesion).
The first surface protective film 8 includes a film substrate 81 and an adhesive layer 82 laminated on the film substrate 81 .

K. Second Surface Protective Film The second surface protective film 9 is a processing material that is temporarily attached during the transportation process of the optical laminate and is peeled off from the first surface protective film 8 before the foreign matter inspection of the optical laminate. The second surface protective film 9 is attached to the film base 81 of the first surface protective film 8.

L. Pressure-sensitive adhesive layer In the illustrated example, the pressure-sensitive adhesive layer 20 is located on the opposite side of the polarizing film 51 with respect to the protective layer 52, and is laminated on the hard coat layer 54. The pressure-sensitive adhesive layer 20 is formed of the same pressure-sensitive adhesive layer 21 as described above.
The thickness of the pressure-sensitive adhesive layer 20 is typically 1 μm or more, preferably 5 μm or more, more preferably 12 μm or more, and typically 60 μm or less, preferably 30 μm or less, more preferably 23 μm or less.

M. Release Liner The release liner 10 is formed of any suitable resin film. Specific examples of materials that are the main components of the resin film include polyethylene terephthalate (PET), polyethylene, and polypropylene. The resin film materials can be used alone or in combination. The release liner 10 can be transparent or non-transparent.

A release treatment layer may be provided on the surface of the release liner 10 that comes into contact with the pressure-sensitive adhesive layer 20. Examples of release treatment agents that form the release treatment layer include silicone-based release treatment agents, fluorine-based release treatment agents, and long-chain alkyl acrylate-based release agents. The release treatment agents may be used alone or in combination. The thickness of the release treatment layer is typically 50 nm or more and 400 nm or less.
The thickness of the release liner 10 is typically 5 μm or more, preferably 20 μm or more, and typically 60 μm or less, preferably 45 μm or less. When a release treatment layer is applied, the thickness of the release liner includes the thickness of the release treatment layer.

N. Image display device The optical laminate described in the above items A to M can be applied to an image display device. More specifically, the second surface protective film 9 is peeled off from the first surface protective film 8, the release liner 10 is peeled off from the adhesive layer 20, and then the optical laminate is attached to an image display element (image display cell) by the adhesive layer 20 and applied to an image display device. Therefore, one embodiment of the present invention also includes an image display device using such an optical laminate. Representative examples of image display devices include liquid crystal display devices and organic EL display devices. The image display device according to the embodiment of the present invention typically includes the optical laminate described in the above items A to M on the viewing side. The image display device includes an image display panel. The image display panel includes an image display element (image display cell). Note that the image display device may be referred to as an optical display device, the image display panel may be referred to as an optical display panel, and the image display cell may be referred to as an optical display cell.
In one embodiment, the optical laminate is applied to an image display device such that the lamination direction is substantially parallel to the thickness direction of the image display panel, thereby stably imparting excellent optical compensation performance to the image display device in the front direction and in an oblique direction intersecting with the front direction.

In one embodiment, the optical laminate may be suitably applied to a retroreflective aerial imaging device (AIRR type aerial display). That is, the optical laminate 100 is preferably an optical laminate for a retroreflective aerial imaging device.
5, a retroreflective aerial imaging device 102 (hereinafter simply referred to as aerial imaging device 102) includes a display element 25, the above-mentioned optical laminate 100, a beam splitter 26, a retroreflective sheet 27, and a λ/4 retardation plate 28. In the illustrated example, the display element 25, the beam splitter 26, and the retroreflective sheet 27 are arranged in a generally triangular shape in a side view.

The display element 25 has a display surface for displaying an image. Examples of the display element 25 include a liquid crystal display and an organic EL display.
The optical laminate 100 is provided between the display element 25 and the beam splitter 26. The optical laminate 100 is typically attached to the display surface of the display element 25. More specifically, after the second surface protective film 9 is peeled off from the first surface protective film 8 and the release liner 10 is peeled off from the adhesive layer 20, the optical laminate is attached to the display element 25 by the adhesive layer 20. Light corresponding to an image displayed on the display element 25 is incident on the optical laminate 100. The optical laminate 100 converts the light (random light) of the display element 25 incident from all directions into circularly polarized light in a first rotation direction.

When the optical laminate is applied to an aerial imaging device, the lamination direction of the optical laminate 100 is typically substantially parallel to the direction perpendicular to the display surface. In the optical laminate 100, the multiple phase difference members are located on the opposite side of the display element 25 with respect to the polarizing member 5. When the multiple phase difference members include a first phase difference member 1, a second phase difference member 2, a third phase difference member 3, and a fourth phase difference member 4, the first phase difference member 1, the second phase difference member 2, the third phase difference member 3, and the fourth phase difference member 4 are arranged in this order from the beam splitter 26 side. When the multiple phase difference members include a first phase difference member 1, a second phase difference member 2, and a fifth phase difference member 50, the first phase difference member 1, the second phase difference member 2, and the fifth phase difference member 50 are arranged in this order from the beam splitter 26 side.

Beam splitter 26 is a circular polarizing beam splitter that selectively reflects circularly polarized light in a first rotation direction and selectively transmits circularly polarized light in a second rotation direction opposite to the first rotation direction. Beam splitter 26 is composed of, for example, cholesteric liquid crystal. The angle between beam splitter 26 and display element 25 is typically within 45°±5°.

The retroreflective sheet 27 can retroreflect the light reflected by the beam splitter 26 back towards the beam splitter 26 (reflecting the light from the beam splitter in a direction opposite to the incident direction). Any appropriate configuration can be adopted for the retroreflective sheet 27. Examples of retroreflective sheets include a bead type and a prism type. The angle between the retroreflective sheet 27 and the display element 25 is typically within 90°±5°.

The λ/4 retardation plate 28 is disposed between the retroreflective sheet 27 and the beam splitter 26. The λ/4 retardation plate 28 is typically provided on the surface of the retroreflective sheet 27 on the beam splitter side. The λ/4 retardation plate 28 typically has a refractive index of nx>ny≧nz. Here, "ny=nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. The in-plane retardation Re(550) of the λ/4 retardation plate 28 is, for example, 100 nm to 200 nm, and preferably 130 nm to 150 nm.
The thickness of the λ/4 phase difference plate 28 is set so as to have an appropriate function as a λ/4 plate. The thickness of the λ/4 phase difference plate 28 is, for example, 20 to 100 μm, preferably 20 to 60 μm, and more preferably 30 to 50 μm.

Next, the formation of an aerial image in the aerial imaging device 102 will be described.
In the illustrated aerial imaging device 102, light corresponding to an image displayed on the display element 25 is first incident on the optical stack 100. The optical stack 100 converts the incident light (random light) into circularly polarized light in a first rotation direction and emits the light. Since the ellipticity is equal to or greater than the lower limit, the optical stack 100 can efficiently convert both the light incident along the stacking direction and the light incident in an oblique direction intersecting the stacking direction.
Then, the beam splitter 26 reflects the circularly polarized light in the first rotation direction from the optical laminate 100 toward the retroreflective sheet 27. The circularly polarized light in the first rotation direction reflected by the beam splitter 26 passes through the λ/4 phase difference plate 28 before reaching the retroreflective sheet 27 and after being retroreflected by the retroreflective sheet 27. This reverses the rotation direction of the circularly polarized light. That is, the circularly polarized light in the first rotation direction becomes circularly polarized light in the second rotation direction. Then, the circularly polarized light in the second rotation direction passes through the beam splitter 26 and is imaged at a position that is plane-symmetrical to the display element 25 with respect to the beam splitter 26. As a result, a clear aerial image I is formed.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each characteristic are as follows.

(1) Measurement of Retardation Value The retardation of each of the first to fifth retardation members used in the examples and comparative examples was automatically measured using KOBRA-WPR manufactured by Oji Scientific Instruments Co., Ltd. The measurement wavelength was 550 nm and the measurement temperature was 23°C.
(2) Measurement of ellipticity The ellipticity of the optical laminate obtained in the examples and comparative examples is measured using a high-speed and high-precision Mueller matrix polarimeter (Axometrics, AxoScan).More specifically, the optical laminate is set in the polarimeter, and light with wavelengths of 450 nm, 550 nm, and 650 nm is incident from the polarizing member side at 23 ° C., and light is emitted from the first phase difference member side, and the minor axis radius b/major axis radius a of the emitted light at the azimuth angle and elevation angle shown in Table 1 are measured, and the average value of the minor axis radius b/major axis radius a of the light of the above three kinds of wavelengths is shown in Table 1 as ellipticity.

[Preparation of Polarizing Member]
<Production Example 1>
As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used, and one side of the resin substrate was subjected to a corona treatment.
A PVA aqueous solution (coating solution) was prepared by adding 13 parts by mass of potassium iodide to 100 parts by mass of a PVA-based resin prepared by mixing polyvinyl alcohol (degree of polymerization 4,200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFFIMER") in a ratio of 9:1, and dissolving the resultant in water.
The above PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (machine direction) in an oven at 130° C. (auxiliary in-air stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by mass of boric acid with 100 parts by mass of water) having a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 to 100 parts by mass of water) having a liquid temperature of 30° C. for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizing film would be a desired value (dyeing treatment).
Next, the plate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by mass of potassium iodide and 5 parts by mass of boric acid with respect to 100 parts by mass of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment).
Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4 wt %, potassium iodide concentration: 5 wt %) at a liquid temperature of 70° C., and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by mass of potassium iodide with 100 parts by mass of water) at a liquid temperature of 20° C. (cleaning treatment).
Thereafter, the film was dried in an oven maintained at about 90° C., while being brought into contact with a SUS heated roll whose surface temperature was maintained at about 75° C. (drying shrinkage treatment).
In this manner, a polarizing film having a thickness of about 5 μm was formed on the resin substrate, and a laminate having a resin substrate/polarizing film structure was obtained.
A cellulose-based resin film (thickness: 32 μm) provided with a hard coat layer was attached as a protective layer to the polarizing film surface (the surface opposite to the resin substrate) of the obtained laminate via an ultraviolet-curable adhesive layer. The resin substrate was then peeled off to obtain a polarizing member having a protective layer/polarizing film configuration.

[Preparation of a first phase difference member (positive C plate) having a refractive index of nz>nx=ny]
<Production Example 2>
A liquid crystal coating solution was prepared by dissolving 20 parts by mass of a side-chain liquid crystal polymer represented by the following chemical formula (II) (the numbers 65 and 35 in the formula indicate the mole percentages of the monomer units, and are conveniently represented as a block polymer: weight average molecular weight 5000), 80 parts by mass of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: product name Paliocolor LC242), and 5 parts by mass of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals: product name Irgacure 907) in 200 parts by mass of cyclopentanone.

The coating liquid was then applied to a substrate film (norbornene-based resin film: manufactured by Zeon Corporation, product name "ZEONEX") using a bar coater, and the liquid crystal was aligned by heating and drying for 4 minutes at 80° C. The liquid crystal layer was irradiated with ultraviolet light to harden the liquid crystal layer, thereby forming a first retardation member (first retardation film) having a thickness of 4 μm on the substrate.
The first retardation member thus obtained had a refractive index of nz>nx=ny. The retardation Rth(550) in the thickness direction of the first retardation member (positive C plate) is shown in Table 1.

[Preparation of second phase difference member functioning as a λ/4 plate]
<Production Example 3>
In a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux condenser controlled at 100 ° C., 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by mass (0.200 mol) of isosorbide (ISB), 42.28 parts by mass (0.139 mol) of spiroglycol (SPG), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19 × 10 ^-2 parts by mass (6.78 × 10 -5 mol) of calcium acetate monohydrate as a catalyst were charged. After the inside of the reactor was replaced with nitrogen under reduced pressure, the reactor was heated with a heat medium, and stirring was started when the internal temperature reached 100 ° C. The internal temperature was allowed to reach 220°C 40 minutes after the start of the temperature rise, and the pressure was controlled to maintain this temperature while simultaneously starting decompression, and the pressure was reduced to 13.3 kPa in 90 minutes after reaching 220°C. Phenol vapor by-produced during the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer components contained in the phenol vapor were returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C and recovered. Nitrogen was introduced into the first reactor to restore the pressure to atmospheric pressure once, and the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, the temperature rise and decompression in the second reactor were started, and the internal temperature was set to 240°C and the pressure to 0.2 kPa in 50 minutes. Thereafter, polymerization was allowed to proceed until a predetermined stirring power was reached. Nitrogen was introduced into the reactor at the time the predetermined power was reached to restore the pressure, and the polyester carbonate resin produced was extruded into water, and the strands were cut to obtain pellets.
The obtained polyester carbonate-based resin (pellets) was vacuum-dried at 80°C for 5 hours, and then stretched in the width direction of the roll at a stretching temperature of 150°C using a film-forming device equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder setting temperature: 250°C), a T-die (width 200 mm, setting temperature: 250°C), a chill roll (setting temperature: 120 to 130°C) and a winder, to obtain a second retardation member (second retardation film) having a thickness of 47 μm as described in Table 1.
The second phase difference member thus obtained has an Re(550) of 147 nm and can function as a λ/4 member.

[Preparation of a third phase difference member (positive B plate) having a refractive index of nz>nx>ny]
<Production Example 4>
Hydroxypropylmethylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., trade name Metolose 60SH-50) 48 parts by mass, distilled water 15601 parts by mass, diisopropyl fumarate 8161 parts by mass, 3-ethyl-3-oxetanylmethyl acrylate 240 parts by mass, and t-butyl peroxypivalate 45 parts by mass as a polymerization initiator were added, and after nitrogen bubbling for 1 hour, the mixture was stirred and held at 49°C for 24 hours to carry out radical suspension polymerization. The mixture was then cooled to room temperature, and the suspension containing the produced polymer particles was centrifuged. The obtained polymer was washed twice with distilled water and twice with methanol, and then dried under reduced pressure.
The obtained fumaric acid ester-based resin was dissolved in a toluene-methyl ethyl ketone mixed solution (toluene/methyl ethyl ketone 50% by mass/50% by mass) to prepare a 20% by mass solution. Further, 5 parts by mass of tributyl trimellitate as a plasticizer was added to 100 parts by mass of the fumaric acid ester-based resin to prepare a dope.
The prepared dope was formed into a film of a desired thickness on a biaxially stretched polyester (polyethylene terephthalate/isophthalate copolymer) film (thickness: 75 μm, width: 1350 mm) as a support film, and then dried by heating.
The laminate was set in the unwinding section of a stretching device, and while unwinding and transporting the laminate downstream, the stretching ratio and stretching temperature were adjusted to obtain the retardation values shown in Table 1, and free-end uniaxial stretching was performed in a stretching furnace. The support was peeled off from the laminate after stretching to obtain a third retardation member (third retardation film).
The third retardation member (third retardation film) thus obtained had a refractive index of nz>nx>ny. The in-plane retardation Re(550) and the thickness direction retardation Rth(550) of the third retardation member are shown in Table 1.
<Production Examples 5 to 9>
A third retardation member (third retardation film) having a thickness of 5 μm shown in Table 1 was obtained in the same manner as in Production Example 4, except that the stretching ratio was changed so as to obtain the retardation value shown in Table 1.

[Preparation of a fourth phase difference member (negative B plate) having a refractive index of nx>ny>nz]
<Production Example 10>
A long norbornene-based resin film (manufactured by Zeon Corporation, product name Zeonor, thickness 40 μm, photoelastic coefficient 3.10 × 10 ^-12 m ² /N) was stretched laterally at a fixed end while adjusting the stretching ratio and drying temperature so as to obtain the retardation values shown in Table 1, to produce a fourth retardation member (fourth retardation film) with a thickness of 18 μm.
The fourth retardation member thus obtained had a refractive index of nx>ny>nz. The in-plane retardation Re(550) and the thickness direction retardation Rth(550) of the fourth retardation member are shown in Table 1.
<Production Example 11>
A fourth retardation member shown in Table 1 was obtained in the same manner as in Production Example 10, except that the stretching ratio and drying temperature were changed so as to obtain the retardation value shown in Table 1.

[Preparation of fifth phase difference member (Z film) having refractive index of nx>nz>ny]
<Production Example 12>
A 60 μm thick shrinkable film (Toray Industries, Torayfan BO2873) was attached to one side of a 130 μm thick norbornene resin film (Optes, Zeonor ZF-14-100) via an acrylic adhesive layer (thickness 20 μm). The film was then stretched 1.3 times in an air circulating oven at 146° C. to obtain a laminate in which a fifth retardation member (fifth retardation film) was formed on the shrinkable film. The fifth retardation member was then peeled off from the shrinkable film.
The fifth retardation member thus obtained had a refractive index of nx>nz>ny. The in-plane retardation Re(550) and the Nz coefficient of the fifth retardation member are shown in Table 1.

<<Examples 1 to 7>>
As shown in Table 1, the first phase difference member of Production Example 2, the second phase difference member of Production Example 3, the third phase difference member of any of Production Examples 4 to 9, the fourth phase difference member of Production Example 10 or 11, and the polarizing member (polarizing film/protective layer) of Production Example 1 were laminated in this order. The lamination was performed so that the angle between the absorption axis direction of the polarizer and the slow axis direction of the phase difference member (each of the first phase difference member to the fourth phase difference member) was the value in Table 1. In addition, the first phase difference member and the second phase difference member were bonded together with an ultraviolet-curing adhesive layer (thickness 1 μm). The second phase difference member and the third phase difference member were bonded together with a (meth)acrylic pressure-sensitive adhesive layer (thickness 23 μm). The third phase difference member and the fourth phase difference member were bonded together with an ultraviolet-curing adhesive layer (thickness 1 μm). The fourth phase difference member and the polarizing member (specifically, the polarizing film) were bonded together with an ultraviolet-curing adhesive layer (thickness 1 μm).
In this way, an optical laminate was produced. The obtained optical laminate was subjected to the above-mentioned measurement of ellipticity.

<<Example 8>>
As shown in Table 1, the first phase difference member of Production Example 2, the second phase difference member of Production Example 3, the fifth phase difference member of Production Example 12, and the polarizing member (polarizing film/protective layer) of Production Example 1 were laminated in this order. The lamination was performed so that the angle between the absorption axis direction of the polarizer and the slow axis direction of the phase difference members (each of the first phase difference member, the second phase difference member, and the fifth phase difference member) was the value in Table 1. In addition, the first phase difference member and the second phase difference member were bonded together with an ultraviolet-curing adhesive layer (thickness 1 μm). The second phase difference member and the fifth phase difference member were bonded together with a (meth)acrylic pressure-sensitive adhesive layer (thickness 23 μm). The fifth phase difference member and the polarizing member (specifically, the polarizing film) were bonded together with an ultraviolet-curing adhesive layer (thickness 1 μm).
In this way, an optical laminate was produced. The obtained optical laminate was subjected to the above-mentioned measurement of ellipticity.

<<Example 9>>
As shown in Table 1, the first phase difference member of Production Example 2, the second phase difference member of Production Example 3, and the polarizing member (polarizing film/protective layer) of Production Example 1 were laminated in this order. The lamination was performed so that the angle between the absorption axis direction of the polarizer and the slow axis direction of the phase difference member (first phase difference member or second phase difference member) was the value shown in Table 1. The first phase difference member and the second phase difference member were bonded together with an ultraviolet-curable adhesive layer (thickness 1 μm). The second phase difference member and the polarizing member (specifically, the polarizing film) were bonded together with an ultraviolet-curable adhesive layer (thickness 1 μm).
In this way, an optical laminate was produced. The obtained optical laminate was subjected to the above-mentioned measurement of ellipticity.

<<Example 10>>
An optical laminate was produced in the same manner as in Example 8, except that the angle between the absorption axis direction of the polarizer and the slow axis direction of the fifth retardation member was changed to the value in Table 1. The obtained optical laminate was subjected to the above-mentioned measurement of ellipticity.

<<Comparative Example 1>>
As shown in Table 1, the second phase difference member of Production Example 3 and the polarizing member of Production Example 1 (polarizing film/protective layer) were laminated in this order. The lamination was performed so that the angle between the absorption axis direction of the polarizer and the slow axis direction of the second phase difference member was the value shown in Table 1. The second phase difference member and the polarizing member (specifically, the polarizing film) were bonded together with an ultraviolet-curing adhesive layer (thickness 1 μm).
In this way, an optical laminate was produced. The obtained optical laminate was subjected to the above-mentioned measurement of ellipticity.

<<Comparative Examples 2 to 4>>
An optical laminate was produced in the same manner as in Example 8, except that the angle between the absorption axis direction of the polarizer and the slow axis direction of the fifth retardation member was changed to the value in Table 1. The obtained optical laminate was subjected to the above-mentioned measurement of ellipticity.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the configurations shown in the above-described embodiments can be replaced with configurations that are substantially the same as those shown in the above-described embodiments, that have the same effects, or that can achieve the same purpose.

The optical laminate of the present invention can be used in image display devices (typically liquid crystal display devices and organic EL display devices), and can be particularly suitably used in retroreflective aerial imaging devices (floating displays).

Reference Signs List 100 Optical laminate 1 First phase difference member 2 Second phase difference member 3 Third phase difference member 4 Fourth phase difference member 5 Polarizing member 51 Polarizing film

Claims

A polarizing member;
a plurality of phase difference members arranged on the viewing side of the polarizing member;
An optical laminate having an ellipticity of 0.75 or more measured at an azimuth angle of 0° and an elevation angle of 90° and an elevation angle of 30°.
The optical laminate of claim 1, in which the ellipticity measured at an azimuth angle of 45° and an elevation angle of 90° and an elevation angle of 30° is 0.70 or more.
The plurality of phase difference members include
A first phase difference member having a refractive index of nz>nx=ny;
A second phase difference member functioning as a λ/4 member;
A third phase difference member having a refractive index of nz>nx≧ny;
3. The optical laminate according to claim 1, further comprising, in this order from the viewing side, a fourth phase difference member having a refractive index of nx>ny≧nz.
The plurality of phase difference members include
A first phase difference member having a refractive index of nz>nx=ny;
A second phase difference member functioning as a λ/4 member;
a fifth phase difference member having a refractive index of nx>nz>ny, in that order from the viewing side;
3. The optical laminate according to claim 1, wherein an angle between the absorption axis direction of the polarizing member and the slow axis direction of the fifth retardation member is 90°±1.5° or less.