Optical laminate and image display device using the same

Abstract

To provide an optical laminate which includes a liquid crystal alignment solidified layer and is capable of suppressing particular display unevenness when used in image display devices.SOLUTION: An optical laminate according to an embodiment of the present invention comprises a polarizing plate including a polarizer, and a retardation layer laminated on the polarizing plate via a first adhesive layer. The retardation layer comprises a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer laminated on the first liquid crystal alignment solidified layer via a second adhesive layer in order from the polarizing plate side. A refractive index nLC1 and a thickness TLC1 of a polarizer of the first liquid crystal alignment solidified layer in a transmission axis direction, a refractive index nAD1 of a polarizer of the first adhesive layer in a transmission axis direction, and a refractive index nAD2 of a polarizer of the second adhesive layer in a transmission axis direction satisfy the following expression (1): {(nAD1-nLC1)2+(nAD2-nLC1)2} / TLC1<0.024 ...(1).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, image display devices represented by liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have been rapidly spreading. In many cases, an optical laminate including a retardation film (for example, an antireflection film in which a polarizing plate and a retardation film are integrated) is used for the image display device. In recent years, as the demand for thinning of the image display device has increased, the demand for thinning of the optical laminate has also increased. For the purpose of thinning the optical laminate, the thinning of the retardation layer (retardation film) that contributes greatly to the thickness has been progressing. As a typical example of the thin retardation film, a film in which a liquid crystal compound is aligned and its alignment state is fixed (hereinafter referred to as a liquid crystal film) can be mentioned. Since the liquid crystal compound has a significantly larger birefringence (Δn) than the resin, the liquid crystal film can have a significantly smaller thickness than the stretched film of the resin film to obtain a desired in-plane retardation. However, in an image display device using an optical laminate including a liquid crystal film, display unevenness (specifically, a phenomenon in which a thin pink line that is particularly noticeable in the absorption axis direction of the polarizer is visually recognized) may occur depending on the viewing environment.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made to solve the above-described conventional problems, and its main object is to provide an optical laminate that includes a liquid crystal alignment cured layer and can suppress specific display unevenness when applied to an image display device.

Means for Solving the Problems

[0005] [1] The optical laminate according to an embodiment of the present invention has a polarizing plate including a polarizer and a retardation layer laminated on the polarizing plate via a first adhesive layer; the retardation layer includes, in order from the polarizing plate side, a first liquid crystal alignment cured layer and a second liquid crystal alignment cured layer laminated on the first liquid crystal alignment cured layer via a second adhesive layer; the refractive index n LC1 and thickness T LC1 of the first liquid crystal alignment cured layer in the transmission axis direction of the polarizer, the refractive index n AD1 of the first adhesive layer in the transmission axis direction of the polarizer, and the refractive index n AD2 of the second adhesive layer in the transmission axis direction of the polarizer satisfy the following formula (1): {(n AD1 - n LC1 ) 2 + (n AD2 - n LC1 ) 2} / T LC1 < 0.024 ···(1). [2] In the above [1], the above n LC1 is greater than 1.60. [3] In the above [1] or [2], the angle formed by the slow axis of the first liquid crystal alignment cured layer and the transmission axis of the polarizer is 40° or less. [4] In any one of the above [1] to [3], the above T LC1 is 1.5 μm or more. [5] In any one of the above [1] to [4], the above T LC1 is 2.0 μm or less. [6] In any one of the above [1] to [5], the optical laminate satisfies the following formula (2): (n AD1 - n LC1 ) 2 + (n AD2 - n LC1 ) 2>0.020 ···(2). [7] In any one of the above [1] to [6], the thickness T of the first adhesive layer AD1 and the thickness T of the second adhesive layer AD2 are each 0.4 μm to 2.0 μm. [8] According to another aspect of the present invention, an image display device is provided. The image display device includes the optical laminate according to any one of the above [1] to [7].

Advantages of the Invention

[0006] According to an embodiment of the present invention, an optical laminate including a liquid crystal alignment solidification layer and capable of suppressing specific display unevenness when applied to an image display device can be realized.

Brief Description of the Drawings

[0007]

Figure 1

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.

[0009] (Definitions of Terms and Symbols) The definitions of the terms and symbols in this specification are as follows. (1) Refractive Index (nx, ny, nz) "nx" is the refractive index in the direction 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 Phase Difference (Re) "Re(λ)" is the in-plane retardation of the film measured with light of wavelength λ nm at 23°C. For example, "Re(550)" is the in-plane retardation of the film measured with light of wavelength 550 nm at 23°C. Re(λ) can be obtained by the formula: Re = (nx - ny) × d, where d (nm) is the thickness of the film. (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction of the film measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction of the film measured with light of wavelength 550 nm at 23°C. Rth(λ) can be obtained by the formula: Rth = (nx - nz) × d, where d (nm) is the thickness of the film. (4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re. (5) Angle When referring to an angle in this specification, unless otherwise specified, the angle includes angles in both the clockwise and counterclockwise directions. Thus, for example, "45°" includes ±45°.

[0010] A. 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 has a polarizing plate 10 and a retardation layer 20 laminated on the polarizing plate 10 via a first adhesive layer 31. The polarizing plate 10 typically includes a polarizer 11 and protective layers 12 and 13 disposed on both sides of the polarizer 11. Depending on the purpose, at least one of the protective layers 12 and 13 may be omitted. Thus, the polarizing plate may be a so-called double-protection polarizing plate, a so-called single-protection polarizing plate, or may be composed of only a polarizer.

[0011] The retardation layer 20 includes, in order from the polarizer 10 side, a first liquid crystal alignment cured layer 21 and a second liquid crystal alignment cured layer 22 laminated on the first liquid crystal alignment cured layer 21 via a second adhesive layer 32. Therefore, in the retardation layer 20, the first liquid crystal alignment cured layer 21 is laminated on the polarizer 10 via the first adhesive layer 31. By using the liquid crystal alignment cured layer as the retardation layer, a desired in-plane retardation can be realized with a thickness significantly thinner than that of the stretched film of the resin film. As a result, the optical laminate can be significantly thinned. In one embodiment, the retardation layer 20 has a circular polarization function or an elliptical polarization function as a whole (as a laminate of the first liquid crystal alignment cured layer 21 and the second liquid crystal alignment cured layer 22). In one embodiment, the retardation layer as a whole may have an Nz coefficient of, for example, 0.30 to 0.70. In this specification, the "liquid crystal alignment cured layer" refers to a layer in which liquid crystal compounds are aligned in a predetermined direction within the layer and the alignment state is fixed. The "liquid crystal alignment cured layer" is a concept that includes an alignment cured layer obtained by curing a liquid crystal monomer.

[0012] In an embodiment of the present invention, the refractive index n in the transmission axis direction of the polarizer of the first liquid crystal alignment cured layer LC1 and the thickness T LC1 , the refractive index n in the transmission axis direction of the polarizer of the first adhesive layer AD1 , and the refractive index n in the transmission axis direction of the polarizer of the second adhesive layer AD2 satisfy the following formula (1). The left side of formula (1) may be referred to as a display unevenness parameter. In the following description of this specification, unless otherwise specified, the "refractive index" means the refractive index in the transmission axis direction of the polarizer. Also, since the first adhesive layer and the first adhesive layer are substantially optically isotropic, the refractive indices n AD1 and n AD2 are also substantially isotropic. {(n AD1 -n LC1 ) 2 +(n AD2 -n LC1 ) 2} / T LC1 <0.024 ···(1) The unevenness parameter is more preferably 0.022 or less, still more preferably 0.020 or less, particularly preferably 0.018 or less, and especially preferably 0.016 or less. The lower limit of the unevenness parameter may be, for example, 0.010, or may be, for example, 0.012.

[0013] In one embodiment, n LC1 , n AD1 and n AD2 satisfy the following formula (2). The left side of formula (2) may be referred to as the refractive index relational expression. The value of the refractive index relational expression may be, for example, 0.024 or more, or may be, for example, 0.027 or more, or may be, for example, 0.029 or more, or may be, for example, 0.030 or more. On the other hand, the value of the refractive index relational expression may be, for example, 0.042 or less, or may be, for example, 0.040 or less. (n AD1 - n LC1 ) 2 +(n AD2 - n LC1 ) 2 > 0.020 ···(2).

[0014] When the inventors considered further thinning of an optical laminate including a liquid crystal alignment solidified layer as a retardation layer, they found a new problem that an image display device using an optical laminate including a liquid crystal alignment solidified layer as a retardation layer may exhibit specific display unevenness depending on the viewing environment. Specifically, in reflection under a three-wavelength light source, they found that a phenomenon may occur in which thin lines with a particularly prominent pink color in the absorption axis direction of the polarizer are visually recognized over the entire area (which may be referred to as line unevenness). Furthermore, when the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer are formed using a material exhibiting positive wavelength dispersion characteristics in which the retardation value decreases as the wavelength of the measurement light increases, even when the same material (and thus, a material having the same average refractive index) is used for each layer, the refractive index in the transmission axis direction of the polarizer changes depending on the angle between the transmission axis of the polarizer and the slow axis of the liquid crystal alignment solidified layer, and the degree of line unevenness can change depending on the refractive index in the transmission axis direction of the polarizer. As a result of intensive studies on suppressing such line unevenness, the inventors found that line unevenness can be suppressed by suppressing the interference of the optical laminate. In addition, instead of individually adjusting the average refractive index, thickness, etc. of each layer constituting the optical laminate to suppress the interference of the optical laminate, the inventors adjusted the refractive index in the transmission axis direction of the polarizer of the liquid crystal alignment solidified layer on the polarizer side (for example, the first liquid crystal alignment solidified layer), the first adhesive layer that laminates the polarizer and the retardation layer, and the second adhesive layer that laminates the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer, and further adjusted the thickness of the liquid crystal alignment solidified layer on the polarizer side to make the above display unevenness parameter smaller than a predetermined value, thereby comprehensively suppressing line unevenness in a specific configuration of the optical laminate according to the purpose and / or constituent materials, etc., and completed the present invention. That is, such an effect according to the embodiment of the present invention solves a newly found problem when considering further thinning of an optical laminate including a liquid crystal alignment solidified layer as a retardation layer, and is an unexpectedly excellent effect. Needless to say, the embodiment of the present invention can suppress display unevenness that has been conventionally recognized.

[0015] As the first adhesive layer 31 and the second adhesive layer 32, any appropriate configuration can be adopted as long as the effects according to the embodiments of the present invention can be obtained (specifically, as long as the above display unevenness parameter can be made equal to or less than a predetermined value). For example, the first adhesive layer and the second adhesive layer may each be composed of an adhesive or an adhesive agent. The first adhesive layer and the second adhesive layer are each typically composed of an adhesive agent, and may be composed of, for example, an active energy ray curable adhesive agent.

[0016] In the optical laminate, the total thickness from the first liquid crystal alignment cured layer to the second liquid crystal alignment cured layer (that is, the total thickness of the retardation layer) is preferably 15 μm or less, more preferably 3 μm to 10 μm. According to the embodiment of the present invention, it is possible to solve the problem of linear unevenness newly found in an optical laminate including a very thin liquid crystal alignment cured layer. In addition, if the total thickness from the first liquid crystal alignment cured layer to the second liquid crystal alignment cured layer is within the above range, the total thickness from the polarizing plate to the second liquid crystal alignment cured layer (the substantial total thickness of the optical laminate excluding the thickness of the adhesive for bonding to the image display panel) can be, for example, 100 μm or less, or, for example, 30 μm to 80 μm.

[0017] The optical laminate may be in a sheet form or in a long form. In this specification, "long form" means an elongated shape in which the length is sufficiently long with respect to the width, and includes, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more, the width. The long optical laminate can be wound in a roll shape. The long optical laminate can be produced, for example, by a so-called roll-to-roll process. The sheet-like optical laminate may be produced by cutting a long optical laminate into a predetermined size (typically, a size corresponding to an image display device), or may be produced by bonding each component (each layer) cut into a predetermined size.

[0018] Practically, the optical laminate has an adhesive layer (not shown) as the outermost layer on the side of the second liquid crystal alignment cured layer (image display panel side) and is capable of being attached to the image display panel. In this case, it is preferable that a release liner is temporarily attached to the surface of the adhesive layer until the optical laminate is put into use. By temporarily attaching the release liner, the adhesive layer is protected and the optical laminate can be formed into a roll.

[0019] Hereinafter, the components of the optical laminate will be specifically described.

[0020] B. Polarizer B-1. Polarizing element The polarizing element 11 is typically composed of a polyvinyl alcohol (PVA)-based resin film containing a dichroic substance (e.g., iodine). Examples of the PVA-based resin include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and partially saponified ethylene-vinyl acetate copolymer.

[0021] The PVA-based resin preferably includes an acetoacetyl-modified PVA-based resin. With such a configuration, a polarizing element having a desired mechanical strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5% by weight to 20% by weight, more preferably 8% by weight to 12% by weight, when the total amount of the PVA-based resin is 100% by weight. If the blending amount is within such a range, a polarizing element having more excellent mechanical strength can be obtained.

[0022] The polarizer preferably contains iodide or sodium chloride (which may be collectively referred to as halide). Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. The content of the halide in the polarizer is preferably 5 parts by weight to 20 parts by weight, more preferably 10 parts by weight to 15 parts by weight, based on 100 parts by weight of the PVA-based resin. The halide can be incorporated into the coating liquid for forming the PVA-based resin layer, which is a precursor of the polarizer, in the manufacturing method described later, and can ultimately be introduced into the polarizer. By introducing the halide into the polarizer, the orientation of PVA molecules in the polarizer can be enhanced, so that a polarizer having excellent optical properties (typically, achieving both high polarization degree and high single transmittance) can be realized.

[0023] The polarizer preferably exhibits absorption dichroism at any wavelength in the range of 380 nm to 780 nm. The single transmittance of the polarizer is preferably 41.0% to 46.0%, more preferably 42.0% to 45.0%. The polarization degree of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. According to the embodiment of the present invention, even when the single transmittance is in the above range, the polarization degree can be maintained in such a range.

[0024] The thickness of the polarizer is, for example, 12 μm or less, preferably 10 μm or less, more preferably 1 μm to 8 μm, and even more preferably 3 μm to 7 μm. By combining such a thin polarizer with the liquid crystal alignment curing layer, significant thinning of the optical laminate becomes possible. Also, if the thickness of the polarizer is in the above range, curling during heating can be well suppressed, and good appearance durability during heating can be obtained.

[0025] The polarizer can be produced by any suitable method. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0026] Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as PVA-based films, partially formalized PVA-based films, and ethylene-vinyl acetate copolymer-based partially saponified films, which are subjected to dyeing treatment with dichroic substances such as iodine and dichroic dyes and stretching treatment, and polyene-based oriented 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.

[0027] The above-mentioned dyeing with iodine is performed, for example, by immersing a PVA-based film in an iodine aqueous solution. The stretching ratio of the above-mentioned uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment, or may be performed while dyeing. Also, dyeing may be performed after stretching. If necessary, the PVA-based film is subjected to swelling treatment, cross-linking treatment, washing treatment, drying treatment, etc. For example, by immersing the PVA-based film in water and washing it before dyeing, not only can the dirt and blocking inhibitor on the surface of the PVA-based film be washed, but also the PVA-based film can be swollen to prevent uneven dyeing.

[0028] 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 the present embodiment, 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 the present embodiment, 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 subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, a stretching treatment in water, and a drying shrinkage treatment in this order. 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 or dissolution when immersed in water in the subsequent dyeing process or 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 stretching treatment in water, in which the laminate is immersed 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 a protective layer for the polarizer), or an arbitrary appropriate protective layer according to the purpose may be laminated on the peeling surface obtained by peeling the resin substrate from the resin substrate / polarizer laminate, or on the surface opposite to the peeling 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.

[0029] B-2. Protective Layer The protective layers 12 and 13 are composed of an arbitrary appropriate resin film. Representative materials for forming the resin film include cellulose-based resins such as triacetyl cellulose (TAC), cycloolefin-based resins such as polynorbornene, (meth)acrylic-based resins, polyester-based resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin-based resins such as polyethylene, and polycarbonate-based resins. Representative examples of the (meth)acrylic-based resin include (meth)acrylic-based resins having a lactone ring structure. (Meth)acrylic-based resins having a lactone ring structure are described, for example, in JP-A-2000-230016, JP-A-2001-151814, JP-A-2002-120326, JP-A-2002-254544, and JP-A-2005-146084. The entire descriptions of these publications are incorporated herein by reference. From the viewpoint of ease of profile processing and the like, cellulose-based resins are preferred, and TAC is more preferred. From the viewpoint of obtaining a polarizing plate having low moisture permeability and excellent durability, cycloolefin-based resins and (meth)acrylic-based resins are preferred.

[0030] The optical laminate is typically disposed on the viewing side of an image display device, and the protective layer 12 is typically disposed on its viewing side. Therefore, the protective layer 12 may be surface-treated as necessary. Examples of the surface treatment include hard coat treatment, antireflection treatment, anti-sticking treatment, and antiglare treatment. Further / alternatively, the protective layer 12 may be treated as necessary to improve visibility when viewing through polarized sunglasses (typically, by imparting an (elliptical) polarization function or a very high retardation). By performing such 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.

[0031] In one embodiment, the protective layer 13 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.

[0032] The thicknesses of the protective layers 12 and 13 are each preferably from 10 μm to 80 μm, more preferably from 12 μm to 40 μm, and even more preferably from 15 μm to 35 μm. When the protective layer 12 is surface-treated, the thickness of the protective layer 12 is the thickness including the thickness of the surface treatment layer.

[0033] C. Retardation layer As described above, the retardation layer 20 includes a first liquid crystal alignment cured layer 21 and a second liquid crystal alignment cured layer 22 in order from the polarizer side. For the description of the retardation layer in this section, when simply referred to as the "retardation layer", it means to describe the entire retardation layer, and when simply referred to as the "liquid crystal alignment cured layer", it means to describe the first liquid crystal alignment cured layer and the second liquid crystal alignment cured layer together.

[0034] In one embodiment, Re(550) of the first liquid crystal alignment curing layer is preferably 150 nm to 300 nm, more preferably 200 nm to 270 nm, and even more preferably 220 nm to 260 nm; Re(550) of the second liquid crystal alignment curing layer is preferably 100 nm to 200 nm, more preferably 110 nm to 160 nm, and even more preferably 110 nm to 130 nm. Thus, since both the first liquid crystal alignment curing layer and the second liquid crystal alignment curing layer have an in-plane retardation, they exhibit a refractive index characteristic of nx > ny (positive A plate). The first liquid crystal alignment curing layer and the second liquid crystal alignment curing layer typically exhibit a refractive index characteristic of nx > ny = nz. Here, "ny = nz" includes not only the case where ny and nz are exactly equal, but also the case where ny and nz are substantially equal. That is, the Nz coefficients of the first liquid crystal alignment curing layer and the second liquid crystal alignment curing layer can be 0.9 to 1.1, respectively.

[0035] The thickness of the first liquid crystal alignment curing layer can be adjusted so that the desired in-plane retardation is obtained and the display unevenness parameter can be made smaller than a predetermined value. In one embodiment, the thickness of the first liquid crystal alignment curing layer can be, for example, 1.5 μm to 2.5 μm. Thus, according to the embodiment of the present invention, linear unevenness can be suppressed while making the thickness of the first liquid crystal alignment curing layer thinner than before. The thickness of the second liquid crystal alignment curing layer can be adjusted so that the desired in-plane retardation is obtained. Specifically, the thickness can be, for example, 0.8 μm to 1.5 μm.

[0036] The angle formed by the slow axis of the first liquid crystal alignment curing layer and the transmission axis of the polarizer is, for example, 40° or less, preferably 10° to 20°, more preferably 12° to 18°, and even more preferably 14° to 16°; the angle formed by the slow axis of the second liquid crystal alignment curing layer and the transmission axis of the polarizer is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably 74° to 76°. Note that the angle formed by the slow axis of the first liquid crystal alignment curing layer and the transmission axis of the polarizer and the angle formed by the slow axis of the second liquid crystal alignment curing layer and the transmission axis of the polarizer may be reversed.

[0037] Examples of the liquid crystal compound used for the liquid crystal alignment curing layer include, for example, liquid crystal polymers and liquid crystal monomers. The liquid crystal compound is preferably polymerizable (i.e., a liquid crystal monomer). When the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by polymerizing it after aligning the liquid crystal compound. Here, the polymer formed by polymerization is non-liquid crystalline. Therefore, in the formed liquid crystal alignment curing layer, for example, a transition from 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 liquid crystal alignment curing layer becomes a retardation layer that is not affected by temperature changes and has extremely excellent stability.

[0038] In one embodiment, the liquid crystal alignment curing layer can be formed using a composition containing a polymerizable liquid crystal compound (a polymerizable liquid crystal compound, i.e., a liquid crystal monomer). In this specification, the polymerizable liquid crystal compound contained in the composition refers to a compound having a polymerizable group and having liquid crystallinity. The polymerizable group means a group involved in a polymerization reaction, and is preferably a photopolymerizable group. Here, the photopolymerizable group refers to a group that can participate in a polymerization reaction by active radicals, acids, etc. generated from a photopolymerization initiator. Examples of the liquid crystal monomer include polymerizable mesogenic compounds described in, for example, JP-T-2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, and GB2280445. Specific examples of such polymerizable mesogenic compounds include, for example, LC242 (trade name of BASF), E7 (trade name of Merck), and LC-Sillicon-CC3767 (trade name of Wacker-Chem).

[0039] The mechanism for the expression of liquid crystallinity of the liquid crystal compound may be thermotropic or lyotropic. Also, the constitution of the liquid crystal phase may be a nematic liquid crystal or a smectic liquid crystal. From the viewpoint of ease of production, thermotropic nematic liquid crystals are preferred for liquid crystallinity.

[0040] The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on its type. Specifically, the temperature range is preferably from 40°C to 120°C, more preferably from 50°C to 100°C, and most preferably from 60°C to 90°C.

[0041] The birefringence Δn of the liquid crystal alignment curing layer is preferably 0.06 or more, more preferably 0.08 or more, still more preferably 0.09 or more, and particularly preferably 0.10 or more. The upper limit of Δn can be, for example, 0.13 or can be, for example, 0.12. If Δn is within such a range, a desired in-plane retardation can be realized with a very thin thickness. As a result, it becomes possible to further reduce the thickness of the liquid crystal alignment curing layer and the optical laminate, and ultimately contribute to a significant thinning of the image display device.

[0042] The liquid crystal alignment curing layer may exhibit an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light, may exhibit a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or may exhibit a flat wavelength dispersion characteristic in which the retardation value hardly changes depending on the wavelength of the measurement light. In one embodiment, the liquid crystal alignment curing layer exhibits a positive wavelength dispersion characteristic. In such a case, the effects according to the embodiments of the present invention are remarkable.

[0043] In another embodiment, Re(550) of the first liquid crystal alignment solidification layer 21 is preferably 130 nm to 225 nm, more preferably 140 nm to 220 nm, still more preferably 150 nm to 215 nm, and particularly preferably 170 nm to 210 nm. In this case, the second liquid crystal alignment solidification layer 22 can typically be a positive C-plate. The thickness of the first liquid crystal alignment solidification layer can be adjusted so as to obtain the desired in-plane retardation and to make the display unevenness parameter smaller than a predetermined value. Specifically, the thickness may be, for example, 1.2 μm to 1.9 μm, or may be, for example, 1.5 μm to 1.8 μm. The angle formed between the slow axis of the first liquid crystal alignment solidification layer and the transmission axis of the polarizer is, for example, 40° or less, preferably -10° to +10°, more preferably -5° to +5°, still more preferably -2° to +2°, and particularly preferably about 0°.

[0044] In yet another embodiment, Re(550) of the first liquid crystal alignment solidification layer 21 is preferably 100 nm to 200 nm, more preferably 110 nm to 180 nm, still more preferably 120 nm to 160 nm, and particularly preferably 130 nm to 150 nm. Also in this case, the second liquid crystal alignment solidification layer 22 can typically be a positive C-plate. The thickness of the first liquid crystal alignment solidification layer can be adjusted so as to obtain the desired in-plane retardation. Specifically, the thickness may be, for example, 1.0 μm to 1.6 μm, or may be, for example, 1.1 μm to 1.3 μm. The angle formed between the slow axis of the first liquid crystal alignment solidification layer and the transmission axis of the polarizer is preferably 40° to 50°, more preferably 42° to 48°, still more preferably 44° to 46°, and particularly preferably about 45°.

[0045] The second liquid crystal alignment curing layer (positive C plate) 22 exhibits a refractive index characteristic of nz > nx = ny. The retardation Rth(550) in the thickness direction of the positive C plate is preferably from -20 nm to -300 nm, more preferably from -30 nm to -250 nm, still more preferably from -40 nm to -200 nm, and particularly preferably from -50 nm to -150 nm. Here, "nx = ny" includes not only the case where nx and ny are exactly equal but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re(550) of the positive C plate can be less than 10 nm.

[0046] The positive C plate can be formed, for example, using a composition containing a side-chain type thermotropic liquid crystal polymer. As the side-chain type thermotropic liquid crystal polymer, a copolymer having a liquid crystalline monomer unit represented by the general formula (I) and a non-liquid crystalline monomer unit represented by the general formula (II) is preferably used.

Chemical formula

Chemical formula

[0047] In formula (I), R 1 is a hydrogen atom or a methyl group, R 2 is a cyano group, a fluoro group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms, and X 1 is -CO2- or -OCO-. a is an integer from 1 to 6, and b and c are each independently 1 or 2.

[0048] In formula (II), R 3 is a hydrogen atom or a methyl group, R 4 is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or a group represented by the following general formula (III).

Chemical formula

[0049] In formula (III), R 5 is an alkyl group having 1 to 5 carbon atoms, and d is an integer of 1 to 6.

[0050] As a specific example of the method for forming the positive C plate, the methods described in

[0020] to

[0028] of Japanese Patent Application Laid-Open No. 2002-333642 can be mentioned. In this case, the thickness of the positive C plate is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and still more preferably 0.5 μm to 5 μm.

[0051] Also in the embodiment using the positive C plate, the arrangement order of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer may be reversed. In this case, the angle formed by the slow axis of the liquid crystal alignment solidified layer other than the positive C plate (the liquid crystal alignment solidified layer exhibiting the refractive index characteristic of nx>ny) and the transmission axis of the polarizer can be appropriately set according to the purpose.

[0052] The refractive index (refractive index in the transmission axis direction of the polarizer) n of the first liquid crystal alignment solidified layer LC1 is the refractive index n of the first adhesive layer AD1 and the refractive index n of the second adhesive layer AD2 As long as the above formula (1) is satisfied in the relationship with, any appropriate refractive index can be adopted. The refractive index n of the first liquid crystal alignment solidified layer LC1 is preferably greater than 1.60, more preferably 1.62 to 1.68, and even more preferably 1.64 to 1.66. The average refractive index of the liquid crystal alignment solidified layer typically conforms to the composition of the composition for forming the liquid crystal alignment solidified layer in order to obtain desired optical characteristics. As a result, linear unevenness may occur. According to the embodiment of the present invention, by setting the display unevenness parameter to a predetermined value or less based on the refractive index and thickness of the first liquid crystal alignment solidified layer in the transmission axis direction of the polarizer, linear unevenness can be suppressed. The refractive index (refractive index in the transmission axis direction of the polarizer) n of the second liquid crystal alignment solidified layer LC2 Any appropriate refractive index can be adopted.

[0053] D. Adhesive layer In this section, the first adhesive layer and the second adhesive layer are collectively described as the "adhesive layer". When it is necessary to distinguish between the first adhesive layer and the second adhesive layer, "first" and "second" are specified. Therefore, when expressing the refractive index as "n AD ", it means the refractive index of the "adhesive layer" when the first adhesive layer and the second adhesive layer are collectively regarded as the "adhesive layer"; when expressing as "n AD1 " or "n AD2 ", it means the refractive index of the first adhesive layer or the second adhesive layer respectively. As the adhesive layer, any appropriate configuration can be adopted as long as the display unevenness parameter can be made below a predetermined value. Specifically, as described above, the adhesive layer may be composed of an adhesive or an adhesive agent. Regardless of whether the adhesive layer is an adhesive layer or an adhesive agent layer, the refractive index n AD of the adhesive layer may be, for example, 1.45 or more, or may be, for example, 1.47 or more, or may be, for example, 1.49 or more. On the other hand, the refractive index n AD of the adhesive layer may be, for example, 1.62 or less, or may be, for example, 1.60 or less.

[0054] Typically, the adhesive layer can be composed of an active energy ray-curable adhesive. In this case, the thickness T AD of the adhesive layer is preferably 0.4 μm to 2.0 μm, more preferably 0.8 μm to 1.2 μm.

[0055] The active energy ray-curable adhesive can adopt any appropriate configuration as long as the display unevenness parameter can be made smaller than a predetermined value. By adjusting the number, type, combination, blending amount, etc. of the resin component, curing component, photopolymerization initiator, and additive in the adhesive (adhesive composition), an adhesive (adhesive composition) having a desired refractive index can be obtained to make the display unevenness parameter smaller than the predetermined value. In one embodiment, the adhesive (adhesive composition) may contain a (meth)acrylate containing an aromatic ring skeleton and / or metal oxide particles. Hereinafter, each will be briefly described. Note that since well-known configurations can be adopted for other components (for example, curing components, photopolymerization initiators) that can be contained in the adhesive, specific descriptions are omitted.

[0056] When the adhesive composition contains a (meth)acrylate having an aromatic ring skeleton, an adhesive layer having a desired refractive index can be formed in an embodiment of the present invention. As the (meth)acrylate having an aromatic ring skeleton, it is preferable to use at least one selected from the group consisting of (meth)acrylates having a polycyclic aromatic ring skeleton and (meth)acrylates having two or more aromatic rings. Examples of such (meth)acrylates include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 1-naphthalenemethyl (meth)acrylate, phenoxybenzyl (meth)acrylate, ethylene oxide-modified orthophenylphenol (meth)acrylate, and the reaction product of 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene and (meth)acrylic acid. Among these, it is more preferable to use phenoxybenzyl (meth)acrylate and phenoxyethyl (meth)acrylate, and it is particularly preferable to use phenoxybenzyl (meth)acrylate. When the total amount of the adhesive composition is 100% by mass, the blending amount of the (meth)acrylate having an aromatic ring skeleton is preferably 20% to 90% by mass, and more preferably 30% to 80% by mass.

[0057] Examples of the metal oxide particles include silicon oxide, zirconium oxide, titanium oxide, zinc oxide, antimony pentoxide, tin oxide, aluminum oxide, indium oxide, indium tin oxide, ferric oxide, cerium oxide, yttrium oxide, manganese oxide, holmium oxide, copper oxide, bismuth oxide, cobalt oxide, cobalt tetroxide, iron tetroxide, magnesium oxide, lanthanum oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, erbium oxide, thulium oxide, ytterbium oxide, lutetium oxide, scandium oxide, tantalum pentoxide, niobium pentoxide, iridium oxide, rhodium oxide, ruthenium oxide, and composite oxides formed by combining these. Among these, zirconium oxide and titanium oxide are preferred, and zirconium oxide is particularly preferred. Note that the metal oxide particles may be composed only of the metal oxides listed above, or may contain other components, but it is preferable that the metal oxide occupies the maximum weight as a component in the particles. The shape of the metal oxide particles can be any shape such as spherical, ellipsoidal, cubic, rectangular parallelepiped, or pyramid shape. Note that, as the metal oxide particles, those surface-treated by any appropriate method may be used.

[0058] From the viewpoints of improving the stability of the metal oxide particles in the adhesive composition and improving the refractive index of the adhesive layer, the average particle diameter of the metal oxide particles is preferably 1 nm to 150 nm, and more preferably 1 nm to 50 nm. The average particle diameter of the metal oxide particles can be derived, for example, by the following method: The particles are magnified and observed using a transmission electron microscope (TEM), a field emission transmission electron microscope (FE-TEM), a field emission scanning electron microscope (FE-SEM), etc., and, for example, 1000 particles are randomly selected, the maximum length thereof is measured, and the arithmetic mean thereof is calculated.

[0059] From the viewpoints of improving the stability of the metal oxide particles in the adhesive composition and increasing the refractive index of the adhesive layer, the blending amount of the metal oxide particles is preferably 10% by mass to 50% by mass, more preferably 15% by mass to 40% by mass, when the total amount of the adhesive composition is 100% by mass.

[0060] The adhesive composition may further contain a hydroxyl group-containing (meth)acrylate. With such a configuration, the adhesive strength of the adhesive layer can be further improved. The blending amount of the hydroxyl group-containing (meth)acrylate is preferably 1% by mass to 30% by mass, more preferably 3% by mass to 20% by mass, when the total amount of the adhesive composition is 100% by mass.

[0061] The pressure-sensitive adhesive can adopt any suitable configuration as long as it can make the display unevenness parameter smaller than a predetermined value. By adjusting the type, number, combination, and blending amount of the monomer components of the base polymer in the pressure-sensitive adhesive (pressure-sensitive adhesive composition); the type, number, combination, and blending amount of the crosslinking agent; and the type, number, combination, and blending amount of the additives, a pressure-sensitive adhesive (pressure-sensitive adhesive composition) capable of realizing desired appearance parameters can be prepared. In one embodiment, the monomer components of the base polymer of the pressure-sensitive adhesive (pressure-sensitive adhesive composition) include a heterocyclic ring-containing acrylate and / or an aromatic ring-containing acrylate. Examples of the heterocyclic ring-containing acrylate include acryloylmorpholine. Examples of the aromatic ring-containing acrylate include benzyl acrylate and phenoxybenzyl acrylate.

[0062] E. Image display device The optical laminate described in the above items A to D can be applied to an image display device. Therefore, embodiments of the present invention also include an image display device using such an optical laminate. Representative examples of the image display device include a liquid crystal display device and an organic EL display device. The image display device according to the embodiments of the present invention typically includes the optical laminate described in the above items A to D on its viewing side.

Examples

[0063] 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 and evaluation methods in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0064] (1) Refractive index The adhesives used in the examples and comparative examples were coated on a cycloolefin polymer film (COP film) (thickness 100 μm), the same COP film was laminated on the coated surface, and visible light was irradiated with an active energy ray irradiation device to obtain a cured product layer (single film). For the obtained cured product layer, the in-plane refractive index and the refractive index in the thickness direction were measured using a prism coupler (manufactured by Sirion Technologies, product name "SPA-4000"), and the average value of these was taken as the average refractive index of the adhesive layer. The measurement wavelength was 594 nm and the measurement temperature was 23°C. Furthermore, for the liquid crystal alignment curing layer, the refractive index in the transmission axis direction was determined as follows. The in-plane retardation Re(550) and the thickness direction retardation Rth(550) were measured using Axoscan (manufactured by Axometrics). nx, ny, and nz were calculated from the following simultaneous equations. Re(550)=(nx - ny)×d Nz = Rth(550) / Re(550)=(nx - nz) / (nx - ny) Furthermore, in the ellipse equation (x 2 / a 2 )+(y 2 / b 2 ) = 1, assuming a is nx, b is ny, x and y are the refractive indices in the x direction and y direction at the angle θ direction on the ellipse, and y = tanθ, a system of simultaneous equations was solved with the above nx and ny to calculate the refractive index in the transmission axis direction.

[0065] (2) Thickness Measured with an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., "MCPD9800").

[0066] (3) Linear unevenness The image display devices obtained in the examples and comparative examples were visually observed under a three-wavelength fluorescent lamp in the non-lighting state and evaluated according to the following criteria. 1 (excellent): No linear unevenness was observed even when observing with a polarizing plate attached to the three-wavelength fluorescent lamp. 2 (good): No linear unevenness was observed in the normal observation with a three-wavelength fluorescent lamp. 3 (acceptable): Slight linear unevenness was observed in the normal observation with a three-wavelength fluorescent lamp. 4 (unacceptable): Practically unacceptable linear unevenness was observed in the normal observation with a three-wavelength fluorescent lamp. 5 (defective): Linear unevenness was prominent in the normal observation with a three-wavelength fluorescent lamp.

[0067] [Production Example 1: Preparation of Adhesive A1 Constituting the Adhesive Layer] 10 parts of hydroxyethyl acrylamide (trade name "HEAA", manufactured by KJ Chemicals Co., Ltd.), 4 parts of 2-acetoxyethyl methacrylate (trade name "AAEM", manufactured by Mitsubishi Chemicals Corporation), 60 parts of acryloylmorpholine (trade name "ACMO", manufactured by KJ Chemicals Co., Ltd.), 11 parts of tripropylene glycol diacrylate (trade name "Aronix M-220", manufactured by Toagosei Co., Ltd.), 1 part of 4-vinylphenylboronic acid (manufactured by Fujifilm Wako Pure Chemical Corporation), 10 parts of an acrylic oligomer (trade name "ARUFON UP-1190", manufactured by Toagosei Co., Ltd.), 1 part of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins B.V.), 2 parts of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins B.V.), and 1 part of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) were stirred at 50 °C for 1 hour to prepare Adhesive A1. The refractive index n of Adhesive A1 AD was 1.52.

[0068] [Production Example 2: Preparation of Adhesive A2 Constituting the Adhesive Layer] 60 parts of Ogsoal EA-F5710 (manufactured by Osaka Gas Chemicals Co., Ltd.), 10 parts of Placcel FA1DDM (manufactured by Daicel Corporation), 20 parts of acryloylmorpholine (trade name "ACMO", manufactured by KJ Chemicals Co., Ltd.), 5 parts of ARFON UP-1190 (manufactured by Toagosei Co., Ltd.), 1 part of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins B.V.), 2 parts of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins B.V.), and 2 parts of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) were stirred at 50 °C for 1 hour to prepare Adhesive A2. The refractive index n of Adhesive A2 AD was 1.56.

[0069] [Production Example 3: Preparation of Adhesive A3 Constituting the Adhesive Layer] 25 parts of acryloylmorpholine (trade name "ACMO", manufactured by KJ Chemicals Co., Ltd.), 10 parts of ε-caprolactone-modified 2-hydroxyethyl acrylate (trade name "PLACCEL FA1DDM", manufactured by Daicel Chemical Industries, Ltd.), 10 parts of lauryl acrylate (trade name "Light Acrylate L-A", manufactured by Kyoeisha Chemical Co., Ltd.), 20 parts of isostearyl acrylate (trade name "ISTA", manufactured by Osaka Organic Chemical Industry Co., Ltd.), 15 parts of 1,9-nonanediol diacrylate (trade name "Light Acrylate 1.9ND-A", manufactured by Kyoeisha Chemical Co., Ltd.), 15 parts of an acrylic oligomer (trade name "ARUFON UP-1190", manufactured by Toagosei Co., Ltd.), 1 part of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins B.V.), 2 parts of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins B.V.), and 2 parts of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) were stirred at 50 °C for 1 hour to prepare Adhesive A3. The refractive index n of Adhesive A3 AD was 1.50.

[0070] [Production Example 4: Preparation of Adhesive A4 Constituting the Adhesive Layer] (Preparation of Dispersant) 415 g (1 mol) of tristyrenated phenol and 1 g (0.018 mol) of potassium hydroxide were charged into an autoclave and mixed uniformly. While the reaction system was at 130 °C, 352 g (8 mol) of ethylene oxide (EO) was dropped into the reaction system. After the dropping of ethylene oxide was completed, the pressure was maintained at 0.1 MPa at 130 °C for 1 hour for aging to obtain an 8-mol adduct of EO to tristyrenated phenol. 767 g (1 mol) of the obtained 8-mol adduct of EO to tristyrenated phenol and 152 g (1.3 mol) of sodium monochloroacetate were put into a reactor and stirred to be uniform. Next, 52 g of sodium hydroxide was added under the condition that the reaction system was at 60 °C, then the temperature was raised to 80 °C and aged for 3 hours. After aging, it was cooled to 50 °C, and 117 g (1.2 mol) of 98% sulfuric acid was dropped at the same temperature to obtain a white suspension solution. This white suspension solution was washed with distilled water, and the solvent was distilled off under reduced pressure to obtain a dispersant. (Preparation of Zirconia Dispersion) To 100 parts of a methanol dispersion of zirconium oxide (manufactured by Sakai Chemical Industry Co., Ltd., grade name "SZR-CM", average particle diameter (D50) based on dynamic light scattering method: 8 nm, zirconium oxide solid content concentration: 30%), 1.5 parts of the dispersant obtained above and 28.5 parts of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A"; hereinafter referred to as "POB-A") were added and mixed. Next, the solvent was removed under reduced pressure using a rotary evaporator to obtain a zirconia dispersion which is a monomer dispersion of zirconium oxide. This zirconia dispersion contains zirconium oxide / dispersant / POB-A in a weight ratio of 50 / 2.5 / 47.5. (Preparation of Adhesive A4) 35 parts of zirconia dispersion, 40 parts of "POB-A", 10 parts of 4-hydroxybutyl acrylate, 10 parts of tripropylene glycol diacrylate (trade name "Aronix M-220", manufactured by Toagosei Co., Ltd.), 1 part of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins B.V.), 2 parts of 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins B.V.), and 2 parts of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) were stirred at 50 °C for 1 hour to prepare Adhesive A4. The refractive index n of Adhesive A4 AD was 1.59.

[0071] [Example 1] 1. Production of polarizing plate 1-1. Production of polarizer 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. 13 parts by weight of potassium iodide was added to 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer") at a ratio of 9:1, and the resulting mixture was dissolved in water 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 (longitudinal direction) in an oven at 130 °C (air-assisted stretching treatment). Next, the laminate was immersed in an insolubilization bath with a liquid temperature of 40 °C (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (insolubilization treatment). Next, it was immersed for 60 seconds in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer became a desired value (dyeing treatment). Next, it was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 40°C (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) (crosslinking treatment). Thereafter, while immersing the laminate in a boric acid aqueous 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 (length direction) between rolls with different peripheral speeds so that the total draw 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 weight of potassium iodide with respect to 100 parts by weight 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 long polarizing plate having a resin substrate / polarizer structure was obtained. The single transmittance Ts of the polarizer was 43.3%. The polarizer had an absorption axis in the long direction. Hereinafter, the absorption axis direction (long direction) is referred to as the "0° direction", and the transmission axis direction (width direction) is referred to as the "90° direction".

[0072] 1-2. Fabrication of polarizing plate An HC-COP film was bonded to the surface of the obtained polarizer (the surface opposite to the resin substrate) via an ultraviolet-curing adhesive. The HC-COP film is a film in which an HC layer (thickness 4 μm) is formed on a cycloolefin-based resin (COP) film (thickness 25 μm), and it was bonded so that the COP film was on the polarizer side. The COP film had a Re(550) of 100 nm. Here, the HC-COP film was bonded so that the angle formed by the slow axis of the COP film and the absorption axis of the polarizer was 45°. Next, the resin substrate was peeled off, and a triacetyl cellulose (TAC) film (thickness 25 μm) was bonded to the peeled surface via an ultraviolet-curing adhesive. In this way, a polarizing plate having a configuration of HC layer / COP film (protective layer) / polarizer / TAC film (protective layer) was obtained.

[0073] 2. Preparation of the retardation layer 2-1. Preparation of the first liquid crystal alignment cured layer A photopolymerizable liquid crystal compound showing a nematic liquid crystal phase (BASF's "Paliocolor LC242", the following chemical formula) was dissolved in cyclopentanone to prepare a solution with a solid content concentration of 30% by weight. To this solution, a surfactant (manufactured by BYK Chemie, "BYK-360") and a photopolymerization initiator (manufactured by IGM Resins, "Omnirad907") were added to prepare a liquid crystal composition solution. The addition amounts of the surfactant and the polymerization initiator were 0.01 part by weight and 3 parts by weight, respectively, with respect to 100 parts by weight of the photopolymerizable liquid crystal compound. As the substrate, a biaxially stretched norbornene-based film (Zeonor film manufactured by Zeon Corporation, thickness 33 μm, Re(550) = 135 nm) was prepared. The above liquid crystal composition was coated on this substrate with a bar coater so that Re(550) was 180 nm, and heated at 100 °C for 3 minutes to align the liquid crystal. After cooling to room temperature, under a nitrogen atmosphere, ultraviolet light with an integrated light amount of 400 mJ / cm 2 was irradiated to perform photocuring, and a long laminated body having a configuration of substrate / first liquid crystal alignment cured layer was obtained. The first liquid crystal alignment cured layer was homogeneously aligned, and its thickness T LC1 was 1.5 μm. The slow axis direction of the first liquid crystal alignment cured layer was the 90° direction. [Chemical formula]

[0074] 2-2. Preparation of the Second Liquid Crystal Alignment and Curing Layer 20 parts by weight of a side-chain liquid crystal polymer represented by the following chemical formula (where n = 0.35 and shown as a block polymer for convenience), 80 parts by weight of a polymerizable liquid crystal showing a nematic liquid crystal phase (manufactured by BASF: trade name Paliocolor LC242), and 5 parts by weight of a photoinitiator (Irgacure 907 manufactured by BASF) were dissolved in 200 parts by weight of cyclopentanone to prepare a liquid crystal coating solution. Then, the coating solution was applied to a PET substrate subjected to vertical alignment treatment using a bar coater, and the liquid crystal was aligned by heating and drying at 80°C for 4 minutes. The liquid crystal layer was irradiated with ultraviolet rays to cure the liquid crystal layer, thereby obtaining a long laminated body having a structure of substrate / second liquid crystal alignment and curing layer (positive C plate, thickness 1.0 μm). [Chemical formula]

[0075] 3. Preparation of the Optical Laminate The first liquid crystal alignment and curing layer was bonded to the surface of the TAC film of the polarizing plate via the adhesive A1 (thickness 1 μm) of Production Example 1 as the first adhesive layer, and then the substrate was peeled off. Next, the second liquid crystal alignment and curing layer was bonded to the surface of the first liquid crystal alignment and curing layer via the adhesive A1 (thickness 1 μm) of Production Example 1 as the second adhesive layer, and the substrate was peeled off to obtain a long optical laminate having a structure of polarizing plate / first liquid crystal alignment and curing layer / adhesive layer / second liquid crystal alignment and curing layer. The bonding and peeling were performed by a roll-to-roll process. In the obtained optical laminate, the refractive index n LC1 of the first liquid crystal alignment and curing layer in the transmission axis direction of the polarizer was 1.65, and the refractive index n LC2 of the second liquid crystal alignment and curing layer was 1.53. Furthermore, the refractive index n AD1 of the first adhesive layer was 1.52, and the refractive index n AD2 of the second adhesive layer was 1.52. As a result, the display unevenness parameter was 0.023.

[0076] 4. Fabrication of Image Display Device The cover glass and the optical film on the viewing side of a commercially available liquid crystal display device (manufactured by Apple Inc., trade name "iPad (registered trademark)", IPS mode) were removed, and after cleaning the removal surface, the second liquid crystal alignment cured layer side of the optical laminate obtained above was bonded to the cleaning surface via an acrylic adhesive (thickness 10 μm) to obtain an image display device. The obtained image display device was subjected to the above-mentioned evaluation of "linear unevenness". The results are shown in Table 1.

[0077] [Examples 2 to 3 and Comparative Examples 1 to 3] Thickness T of the first liquid crystal alignment cured layer LC1 An optical laminate and an image display device were obtained in the same manner as in Example 1 except that the thickness T was changed as shown in Table 1. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0078] [Example 4] Thickness T of the first liquid crystal alignment cured layer LC1 An optical laminate and an image display device were obtained in the same manner as in Example 1 except that the thickness T was set to 1.2 μm (Re(550) = 144 nm) and the adhesive A2 (thickness 1 μm) of Production Example 2 was used as the second adhesive layer. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0079] [Examples 5 to 8 and Comparative Example 4] Thickness T of the first liquid crystal alignment cured layer LC1 An optical laminate and an image display device were obtained in the same manner as in Example 4 except that the thickness T was changed as shown in Table 1. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0080] [Example 9] Thickness T of the first liquid crystal alignment cured layer LC1 An optical laminate and an image display device were obtained in the same manner as in Example 1 except that the thickness T was set to 1.2 μm (Re(550) = 144 nm) and the adhesive A2 (thickness 1 μm) of Production Example 2 was used as the first adhesive layer. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0081] [Examples 10 to 13 and Comparative Example 5] Thickness T of the first liquid crystal alignment cured layer LC1 An optical laminate and an image display device were obtained in the same manner as in Example 9 except that the thickness T of the first liquid crystal alignment cured layer was changed as shown in Table 1. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0082] [Example 14] 1. Production of polarizing plate A polarizing plate was produced in the same manner as in Example 1.

[0083] 2. Production of retardation layer Using the same photopolymerizable liquid crystal compound as in Example 1 and in the same manner as in Example 1, a long laminate having a structure of substrate / first liquid crystal alignment cured layer (Re(550) = 230 nm) was obtained. The first liquid crystal alignment cured layer was in a homogeneous alignment, and its thickness was 1.9 μm. The slow axis direction of the first liquid crystal alignment cured layer was the 75° direction. Except for changing the coating thickness, a long laminate of substrate / second liquid crystal alignment cured layer (homogeneous alignment, thickness 1.0 μm, Re(550) = 120 nm) was obtained in the same manner as above. The slow axis direction of the second liquid crystal alignment cured layer was the 15° direction.

[0084] 3. Production of optical laminate An optical laminate having a structure of polarizing plate / first liquid crystal alignment cured layer / adhesive layer / second liquid crystal alignment cured layer was obtained in the same manner as in Example 1, except that the first and second liquid crystal alignment cured layers obtained above were used, the adhesive A3 (thickness 1 μm) of Production Example 3 was used as the first adhesive layer, and the adhesive A4 (thickness 1 μm) of Production Example 4 was used as the second adhesive layer. In the obtained optical laminate, the refractive index n of the first liquid crystal alignment cured layer in the transmission axis direction of the polarizer LC1 was 1.65, and the refractive index n of the second liquid crystal alignment cured layer LC2 was 1.54. Further, the refractive index n of the first adhesive layer AD1 was 1.50, and the refractive index n of the second adhesive layer AD2 was 1.59, and as a result, the display unevenness parameter was 0.014.

[0085] 4. Fabrication of Image Display Device The cover glass and the optical film on the viewing side of a commercially available organic EL display device (manufactured by Samsung Electronics Co., Ltd., product name "Galaxy (registered trademark) A41") were removed, and the removal surface was cleaned. Then, the second liquid crystal alignment cured layer side of the optical laminate obtained above was bonded to the cleaned surface via an acrylic adhesive (thickness: 10 μm) to obtain an image display device. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0086] [Examples 15 to 17] Thickness T of the first liquid crystal alignment cured layer LC1 and refractive index n of the second adhesive layer AD2 An optical laminate and an image display device were obtained in the same manner as in Example 14 except that they were changed as shown in Table 1. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0087]

Table 1

[0088] In Table 1, for example, "Ex. 1" means Example 1, and "Comp. 1" means Comparative Example 1. Also, "Pos. A" means a positive A plate, and "Pos. C" means a positive C plate.

Industrial Applicability

[0089] The optical laminate according to the embodiment of the present invention can be suitably used for an image display device (typically, a liquid crystal display device, an organic EL display device).

Explanation of Reference Numerals

[0090] 10 Polarizing plate 11 Polarizer 12 Protective layer 13 Protective layer 20 Retardation layer 21 First liquid crystal alignment cured layer 22 Second liquid crystal alignment cured layer 31 First adhesive layer 32 Second adhesive layer 100 Optical laminate

Claims

Claim 1 A polarizing plate including a polarizer, and a retardation layer laminated on the polarizing plate via a first adhesive layer, wherein the retardation layer includes, in order from the polarizing plate side, a first liquid crystal alignment cured layer, and a second liquid crystal alignment cured layer laminated on the first liquid crystal alignment cured layer via a second adhesive layer, The refractive index n in the transmission axis direction of the polarizer of the first liquid crystal alignment curing layer ＬＣ１ and the thickness T ＬＣ１ , the refractive index n in the transmission axis direction of the polarizer of the first adhesive layer ＡＤ１ , and the refractive index n in the transmission axis direction of the polarizer of the second adhesive layer ＡＤ２ satisfy the following formula (1), an optical laminate: {(n ＡＤ１ - n ＬＣ１ ) ２ +(n ＡＤ２ - n ＬＣ１ ) ２} / T ＬＣ１ < 0.024...(1). Claim 2 The above-mentioned n ＬＣ１ The optical laminate according to claim 1, wherein n is greater than 1.

60. Claim 3 The optical laminate according to claim 1, wherein an angle formed between the slow axis of the first liquid crystal alignment cured layer and the transmission axis of the polarizer is 40° or less. Claim 4 The above-mentioned T ＬＣ１ The optical laminate according to claim 1, wherein the above-mentioned T is 1.5 μm or more. Claim 5 The above-mentioned T ＬＣ１ The optical laminate according to claim 4, wherein the above-mentioned T is 2.0 μm or less. Claim 6 The optical laminate according to claim 1, satisfying the following formula (2): (n ＡＤ１ - n ＬＣ１ ) ２ + (n ＡＤ２ - n ＬＣ１ ) ２ > 0.020... (2). Claim 7 The thickness T of the first adhesive layer ＡＤ１ and the thickness T of the second adhesive layer ＡＤ２ are each 0.4 μm to 2.0 μm, and the optical laminate according to claim 1. Claim 8 An image display device including the optical laminate according to any one of claims 1 to 7.

Images