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 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. 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 an adhesive layer in order from the polarizing plate side. A refractive index nLC1 of a polarizer of the first liquid crystal alignment solidified layer in a transmission axis direction, a refractive index nLC2 of a polarizer of the second liquid crystal alignment solidified layer in a transmission axis direction, and a refractive index nAD of a polarizer of the adhesive layer in a transmission axis direction satisfy the following expression (1): (nLC1-nAD)2+(nLC2-nAD)2<0.01 ...(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 typified 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 image display devices has increased, there has also been an increasing demand for thinning of optical laminates. For the purpose of thinning the optical laminate, the retardation layer (retardation film) that contributes greatly to the thickness has been thinned. As a typical example of a 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 including a liquid crystal alignment cured layer and capable of suppressing 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; the retardation layer includes, in order from the polarizer 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 an adhesive layer; the refractive index n LC1 in the transmission axis direction of the polarizer of the first liquid crystal alignment cured layer, the refractive index n LC2 in the transmission axis direction of the polarizer of the second liquid crystal alignment cured layer, and the refractive index n AD in the transmission axis direction of the polarizer of the adhesive layer satisfy the following formula (1): (n LC1 - n AD ) 2 + (n LC2 - n AD ) 2 < 0.01 ···(1). [2] In the above [1], the optical laminate satisfies the following formula (2): (n LC1 - n AD ) 2 + (n LC2 - n AD ) 2 < 0.006 ···(2). [3] In the above [1] or [2], the above n LC1 or the above n LC2 is greater than 1.60. [4] In any one of the above [1] to [3], both the first liquid crystal alignment cured layer and the second liquid crystal alignment cured layer exhibit a refractive index characteristic of nx > ny. [5] In any one of the above [1] to [4], the thickness T AD of the adhesive layer is 0.4 μm to 2.0 μm. [6] In any one of the above [1] to [5], the adhesive layer is composed of an active energy ray curable adhesive. [7]According to another aspect of the present invention, an image display device is provided. The image display device includes any one of the optical laminate bodies described in [1] to [6] above.

Effect of the Invention

[0006] According to an embodiment of the present invention, it is possible to realize an optical laminate body that includes a liquid crystal alignment solidification layer and can suppress specific display unevenness when applied to an image display device.

Brief Description of the Drawings

[0007]

Figure 1

Mode 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] (Definition of Terms and Symbols) The definitions of terms and symbols in this specification are as follows. (1) Refractive Index (nx, ny, nz) “nx” is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and “nz” is the refractive index in the thickness direction. (2) In-Plane Phase Difference (Re) “Re(λ)” is the in-plane phase difference of the film measured with light of wavelength λ nm at 23°C. For example, “Re(550)” is the in-plane phase difference of the film measured with light of wavelength 550 nm at 23°C. Re(λ) is obtained by the formula: Re = (nx - ny) × d, where d is the thickness of the film in nm. (3) Phase Difference 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. Therefore, 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. The polarizing plate 10 and the retardation layer 20 are laminated via an arbitrary appropriate adhesive layer (for example, an adhesive layer, an adhesive layer: not shown). 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. Therefore, 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 the 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 to the first liquid crystal alignment cured layer 21 via an adhesive layer 25. 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, a remarkable thinning of the optical laminate can be achieved. The retardation layer 20, in one embodiment, 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). The retardation layer, in one embodiment, has an Nz coefficient of, for example, 0.30 to 0.70 as a whole. In the present 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 , the refractive index n in the transmission axis direction of the polarizer of the second liquid crystal alignment cured layer LC2 , and the refractive index n in the transmission axis direction of the polarizer of the adhesive layer AD satisfy the following formula (1), and preferably satisfy the following formula (2). The left side of formulas (1) and (2) may be referred to as a display unevenness parameter. In the following description of the present specification, unless otherwise specified, the "refractive index" means the refractive index in the transmission axis direction of the polarizer. Also, since the adhesive layer is substantially optically isotropic, the refractive index n AD is also substantially isotropic. (n LC1 - n AD ) 2 + (n LC2 - n AD ) 2 < 0.01 ···(1) (n LC1 - n AD ) 2 + (n LC2 - n AD ) 2 < 0.006 ···(2) The display unevenness parameter is more preferably 0.005 or less, still more preferably 0.004 or less, particularly preferably 0.003 or less, and especially preferably 0.002 or less. The smaller the display unevenness parameter, the more preferable it is, and it can be, for example, 0.000.

[0013] 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, they found that in reflection under a three-wavelength light source, a phenomenon (sometimes referred to as line unevenness) may occur in which thin lines with a particularly prominent pink color in the absorption axis direction of the polarizer are visually recognized throughout. Furthermore, when the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer are configured 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 formed 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 two liquid crystal alignment solidified layers and the refractive index in the transmission axis direction of the adhesive layer for laminating them to make the above display unevenness parameter smaller than a predetermined value, and found that line unevenness can be comprehensively suppressed in a specific configuration of the optical laminate according to the purpose and / or constituent materials, etc., thus completing the present invention. That is, such an effect according to an 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.

[0014] As the adhesive layer 25, 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 smaller than a predetermined value). For example, the adhesive layer may be composed of an adhesive or may be composed of an adhesive. The adhesive layer is typically composed of an adhesive, and may be composed of, for example, an active energy ray-curable adhesive.

[0015] 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, and more preferably 3 μm to 10 μm. According to the embodiments 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, and can also be, for example, 30 μm to 80 μm.

[0016] The optical laminate may be in a sheet form or in a long strip form. In this specification, "long strip 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 strip-shaped optical laminate can be wound into a roll. The long strip-shaped optical laminate can be produced, for example, by a so-called roll-to-roll process. The sheet-shaped optical laminate may be produced by cutting a long strip-shaped 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.

[0017] 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 can be 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.

[0018] Hereinafter, the components of the optical laminate will be specifically described.

[0019] B. Polarizing plate B-1. Polarizer The polarizer 11 is typically composed of a polyvinyl alcohol (PVA)-based resin film containing a dichroic substance (for example, iodine). Examples of the PVA-based resin include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and ethylene-vinyl acetate copolymer-based partially saponified products.

[0020] The PVA-based resin preferably includes an acetoacetyl-modified PVA-based resin. With such a configuration, a polarizer having desired mechanical strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5% to 20% by weight, more preferably 8% 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 polarizer having more excellent mechanical strength can be obtained.

[0021] 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 to 20 parts by weight, more preferably 10 to 15 parts by weight, based on 100 parts by weight of the PVA-based resin. The halide can be incorporated into the coating solution 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, the coexistence of high polarization degree and high single transmittance) can be realized.

[0022] 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.

[0023] The thickness of the polarizer is, for example, 12 μm or less, preferably 10 μm or less, more preferably 1 to 8 μm, and even more preferably 3 to 7 μm. By combining such a thin polarizer with the liquid crystal alignment curing layer, significant thinning of the optical laminate becomes possible. Further, 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.

[0024] 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.

[0025] 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.

[0026] The above-mentioned dyeing with iodine is carried out, 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 carried out after the dyeing treatment, or may be carried out while dyeing. Also, dyeing may be carried out after stretching. If necessary, the PVA-based film is subjected to swelling treatment, crosslinking 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 anti-blocking agent on the surface of the PVA-based film be washed, but also the PVA-based film can be swollen to prevent uneven dyeing.

[0027] 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 air stretching the laminate at a high temperature (for example, 95°C or higher) before stretching in the aqueous boric acid solution, if necessary. In addition, in the present embodiment, preferably, the laminate is subjected to a dry 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, an underwater stretching treatment, and a dry shrinkage treatment in this order. By introducing the auxiliary stretching, even when PVA is applied on a thermoplastic resin, it becomes possible to enhance the crystallinity of PVA and achieve high optical properties. At the same time, by enhancing the orientation of PVA in advance, problems such as a decrease in the orientation of PVA and dissolution when immersed in water in the subsequent dyeing process and stretching process can be prevented, and high optical properties can be achieved. Further, when the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation and the decrease in the orientation of polyvinyl alcohol molecules 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 an underwater stretching treatment, in which the laminate is immersed in a liquid, can be improved. Furthermore, by shrinking the laminate in the width direction by the dry 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 disclosures of these publications are incorporated herein by reference.

[0028] B-2. Protective Layer The protective layers 12 and 13 are composed of an arbitrary appropriate resin film. Representative materials constituting 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 disclosures of these publications are incorporated herein by reference. From the viewpoint of ease of profile processing and the like, cellulose-based resins are preferable, and TAC is more preferable. From the viewpoint of obtaining a polarizing plate having low moisture permeability and excellent durability, cycloolefin-based resins and (meth)acrylic-based resins are preferable.

[0029] 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 subjected to a treatment (typically, imparting an (elliptical) polarization function or imparting an ultra-high retardation) to improve visibility when viewing through polarized sunglasses as necessary. By performing such a treatment, excellent visibility can be achieved even when viewing the display screen through a polarizing lens such as polarized sunglasses. Therefore, the optical laminate can be suitably applied to an image display device that can be used outdoors.

[0030] 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.

[0031] 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 still 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.

[0032] 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. Regarding the description of the retardation layer in this section, simply referring to the "retardation layer" means describing the entire retardation layer, and simply referring to the "liquid crystal alignment cured layer" means collectively describing the first liquid crystal alignment cured layer and the second liquid crystal alignment cured layer.

[0033] In one embodiment, Re(550) of the first liquid crystal alignment and solidification 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 and solidification 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 and solidification layer and the second liquid crystal alignment and solidification layer have an in-plane retardation, they exhibit a refractive index characteristic of nx > ny. The first liquid crystal alignment and solidification layer and the second liquid crystal alignment and solidification layer typically exhibit a refractive index characteristic of nx > ny = nz (positive A plate). 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 and solidification layer and the second liquid crystal alignment and solidification layer can be 0.9 to 1.1, respectively.

[0034] The thickness of the first liquid crystal alignment and solidification layer can be adjusted so as to obtain the desired in-plane retardation. In one embodiment, the thickness of the first liquid crystal alignment and solidification 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 reducing the thickness of the first liquid crystal alignment and solidification layer as compared with the prior art. The thickness of the second liquid crystal alignment and solidification layer can also be adjusted so as to obtain the desired in-plane retardation. Specifically, the thickness can be, for example, 0.8 μm to 1.5 μm.

[0035] The angle formed by the slow axis of the first liquid crystal alignment and solidification layer and the transmission axis of the polarizer is 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 and solidification 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 and solidification layer and the transmission axis of the polarizer and the angle formed by the slow axis of the second liquid crystal alignment and solidification layer and the transmission axis of the polarizer may be reversed.

[0036] Examples of liquid crystal compounds used for the liquid crystal alignment cured 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 cured layer, for example, phase transitions to a liquid crystal phase, a glass phase, and a crystal phase due to temperature changes peculiar to liquid crystalline compounds do not occur. As a result, the liquid crystal alignment cured layer becomes a retardation layer that is not affected by temperature changes and is extremely stable.

[0037] In one embodiment, the liquid crystal alignment cured 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 with the trade name of BASF, E7 with the trade name of Merck, and LC-Sillicon-CC3767 with the trade name of Wacker-Chem.

[0038] The mechanism for the expression of liquid crystallinity of the liquid crystal compound may be thermotropic or lyotropic. Also, as the constitution of the liquid crystal phase, it 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.

[0039] 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.

[0040] The birefringence Δn of the liquid crystal alignment cured 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 in such a range, a desired in-plane retardation can be realized with a very thin thickness. As a result, the liquid crystal alignment cured layer and the optical laminate can be made thinner, and ultimately can contribute to a significant thinning of the image display device.

[0041] The liquid crystal alignment cured 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 cured layer exhibits a positive wavelength dispersion characteristic. In such a case, the effects according to the embodiments of the present invention are remarkable.

[0042] In another embodiment, Re(550) of the first liquid crystal alignment cured layer 21 is preferably from 100 nm to 200 nm, more preferably from 110 nm to 180 nm, still more preferably from 120 nm to 160 nm, and particularly preferably from 130 nm to 150 nm. In this case, the second liquid crystal alignment cured layer 22 can typically be a positive C-plate. The thickness of the first liquid crystal alignment cured layer can be adjusted so as to obtain the desired in-plane retardation. Specifically, the thickness can be, for example, from 1.0 μm to 1.6 μm, or can be, for example, from 1.1 μm to 1.3 μm. The angle formed between the slow axis of the first liquid crystal alignment cured layer and the transmission axis of the polarizer is preferably from 40° to 50°, more preferably from 42° to 48°, still more preferably from 44° to 46°, and particularly preferably about 45°.

[0043] In still another embodiment, Re(550) of the first liquid crystal alignment cured layer 21 is preferably from 80 nm to 160 nm, more preferably from 90 nm to 150 nm, still more preferably from 100 nm to 140 nm, and particularly preferably from 110 nm to 130 nm. Also in this case, the second liquid crystal alignment cured layer 22 can typically be a positive C-plate. The thickness of the first liquid crystal alignment cured layer can be adjusted so as to obtain the desired in-plane retardation. Specifically, the thickness may be, for example, from 0.8 μm to 1.2 μm, or may be, for example, from 0.9 μm to 1.1 μm. The angle formed by the slow axis of the first liquid crystal alignment cured layer and the transmission axis of the polarizer is, for example, 40° or less, preferably from -10° to +10°, more preferably from -5° to +5°, still more preferably from -2° to +2°, and particularly preferably about 0°.

[0044] The second liquid crystal alignment cured 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.

[0045] 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

[0046] In formula (I), R 1 is a hydrogen atom or a methyl group, and 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.

[0047] In formula (II), R 3 is a hydrogen atom or a methyl group, and 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

[0048] In formula (III), R 5 is an alkyl group having 1 to 5 carbon atoms, and d is an integer from 1 to 6.

[0049] As a specific example of the method for forming the positive C plate, the methods described in

[0020] to

[0028] of JP-A-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 even more preferably 0.5 μm to 5 μm.

[0050] Even 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 showing the refractive index characteristic of nx>ny) and the transmission axis of the polarizer can be appropriately set according to the purpose.

[0051] The refractive index of the liquid crystal alignment solidified layer (the refractive index in the direction of the transmission axis of the polarizer) is the refractive index n of the adhesive layer ADAs long as the above formula (1) is satisfied in the relationship therewith, any appropriate refractive index can be adopted. As described above, when the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer are formed using a material having positive wavelength dispersion characteristics, even if the same material (therefore, 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. Therefore, in the embodiment of the present invention, instead of the average refractive index of the liquid crystal alignment solidified layer, the refractive index in the transmission axis direction of the polarizer can be optimized so as to satisfy the above formula (1). The refractive index n LC1 of the first liquid crystal alignment solidified layer and the refractive index n LC2 of the second liquid crystal alignment solidified layer may be the same or different from each other (the refractive index n LC1 of the first liquid crystal alignment solidified layer may be larger, or the refractive index n LC2 of the second liquid crystal alignment solidified layer may be larger). The refractive index n LC1 of the first liquid crystal alignment solidified layer and the refractive index n LC2 of the second liquid crystal alignment solidified layer are each preferably 1.50 or more, more preferably 1.52 to 1.68, and still more preferably 1.53 to 1.65. In one embodiment, the refractive index n LC1 of the first liquid crystal alignment solidified layer or the refractive index n LC2 of the second liquid crystal alignment solidified layer may be, for example, greater than 1.60. The average refractive index of the liquid crystal alignment solidified layer will typically conform to the composition of the composition for forming the liquid crystal alignment solidified layer in order to obtain the desired optical properties. As a result, line unevenness may occur. According to the embodiment of the present invention, line unevenness can be suppressed by making the display unevenness parameter smaller than a predetermined value based on the refractive index in the transmission axis direction of the polarizer of the liquid crystal alignment solidified layer.

[0052] D. Adhesive layer As the adhesive layer 25, any appropriate configuration can be adopted as long as the display unevenness parameter can be made smaller than a predetermined value. Specifically, as described above, the adhesive layer may be composed of an adhesive or may be composed of a pressure-sensitive adhesive. Regardless of whether the adhesive layer is an adhesive layer or a pressure-sensitive adhesive layer, the refractive index n of the adhesive layer AD may be, for example, 1.45 or more, may be, for example, 1.50 or more, may be, for example, 1.53 or more, may be, for example, 1.55 or more, or may be, for example, 1.57 or more. On the other hand, the refractive index n of the adhesive layer AD can be, for example, 1.63 or less.

[0053] Typically, the adhesive layer can be composed of an active energy ray-curable adhesive. In this case, the thickness T of the adhesive layer AD is preferably 0.4 μm to 2.0 μm, more preferably 0.8 μm to 1.2 μm.

[0054] As long as the active energy ray-curable adhesive can make the display unevenness parameter smaller than a predetermined value, any appropriate configuration can be adopted. By adjusting the number, type, combination, blending amount, etc. of the resin component, curing component, photoinitiator, 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 a predetermined value. In one embodiment, the adhesive (adhesive composition) may contain a (meth)acrylate containing an aromatic ring skeleton and / or metal oxide particles. Each will be briefly described below. Note that for other components that may be included in the adhesive (such as the curing component, photoinitiator), well-known configurations can be adopted, so specific descriptions are omitted.

[0055] By containing a (meth)acrylate having an aromatic ring skeleton in the adhesive composition, 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 a (meth)acrylate having a polycyclic aromatic ring skeleton and a (meth)acrylate 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.

[0056] 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. 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. As the metal oxide particles, those surface-treated by any appropriate method may be used.

[0057] From the viewpoint 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, their maximum length is measured, and the arithmetic mean is calculated to obtain the average particle diameter.

[0058] From the viewpoint of improving the stability of the metal oxide particles in the adhesive composition and the refractive index of the adhesive layer, the compounding 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.

[0059] 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 compounding 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.

[0060] The pressure-sensitive adhesive can adopt any appropriate configuration as long as the display unevenness parameter can be made smaller than a predetermined value. By adjusting the type, number, combination, and compounding amount of the monomer components of the base polymer in the pressure-sensitive adhesive (pressure-sensitive adhesive composition); the type, number, combination, and compounding amount of the crosslinking agent; and the type, number, combination, and compounding amount of the additive, 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.

[0061] E. Image display device The optical laminate described in the above items A to D can be applied to an image display device. Therefore, the embodiments of the present invention also include an image display device using such an optical laminate. Representative examples of the image display device include a liquid crystal display device 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

[0062] 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.

[0063] (1) Refractive index The adhesives used in the examples and comparative examples were applied to a cycloolefin-based polymer film (COP film) (thickness 100 μm), and the same COP film was laminated on the coated surface, and then irradiated with visible light using 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 cured 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, let a be nx, b be ny, x and y be the refractive indices in the x direction and y direction at the angle θ direction on the ellipse, and solve the simultaneous equations from y = tanθ and the above nx and ny to calculate the refractive index in the transmission axis direction.

[0064] (2) Thickness Measured with an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., "MCPD9800").

[0065] (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. ◎ (Excellent): No linear unevenness was observed even when observing with a polarizing plate attached to the three-wavelength fluorescent lamp. ○ (Good): No linear unevenness was observed in the normal observation with the three-wavelength fluorescent lamp. △ (Unacceptable): Linear unevenness was observed in the normal observation with the three-wavelength fluorescent lamp. × (Poor): Linear unevenness was prominent in the normal observation with the three-wavelength fluorescent lamp.

[0066] [Production Example 1: Preparation of Adhesive A1 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 diethylthiioxanthone (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 1.50.

[0067] [Production Example 2: Preparation of Adhesive A2 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 A2. The refractive index n of Adhesive A2 AD was 1.52.

[0068] [Production Example 3: Preparation of Adhesive A3 Constituting the Adhesive Layer] 60 parts of Ogsool 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 A3. The refractive index n of Adhesive A3 AD was 1.56.

[0069] [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.

[0070] [Production Example 5: Preparation of Adhesive A5 Constituting the Adhesive Layer] 55 parts of zirconia dispersion, 25 parts of "POB-A", 10 parts of 4-hydroxybutyl acrylate, 10 parts of "ARONIX M-220", 1 part of "Omnirad 819", 2 parts of "Omnirad 184", and 2 parts of "KAYACURE DETX-S" were stirred at 50 °C for 1 hour to prepare Adhesive A5. The refractive index n of Adhesive A5 AD was 1.61.

[0071] [Example 1] 1. Preparation of Polarizing Plate 1-1. Preparation of Polarizer As a thermoplastic resin substrate, an amorphous isophthalic copolyethylene terephthalate film (thickness: 100 μm) that is long and has 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, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer") in 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 (length direction) in an oven at 130 °C (air-assisted stretching treatment). Next, the laminate was immersed in an insolubilization bath at a liquid temperature of 40 °C (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (insolubilization treatment). Next, the laminate was immersed in a dyeing bath at a liquid temperature of 30 °C (an aqueous iodine solution obtained by blending iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer becomes a desired value (dyeing treatment). Next, the laminate was immersed in a crosslinking bath at a liquid temperature of 40 °C (an aqueous boric acid solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (crosslinking treatment). Thereafter, while the laminate was immersed in an aqueous boric acid solution at a liquid temperature of 70 °C (boric acid concentration 4 wt%, potassium iodide concentration 5 wt%), uniaxial stretching was performed in the longitudinal direction (length direction) between rolls with different peripheral speeds so that the total stretching ratio became 5.5 times (stretching treatment in water). Thereafter, the laminate was immersed in a washing bath at a liquid temperature of 20 °C (an aqueous solution obtained by blending 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. Production of polarizing plate An HC-COP film was laminated onto the surface of the obtained polarizer (the side opposite to the resin substrate) via an ultraviolet-curable 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 laminated such that the COP film was on the polarizer side. The Re(550) of the COP film was 100 nm. Here, the HC-COP film was laminated such 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 laminated onto the peeled surface via an ultraviolet-curable adhesive. In this way, a polarizing plate having a structure of HC layer / COP film (protective layer) / polarizer / TAC film (protective layer) was obtained.

[0073] 2. Preparation of the retardation 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. A surfactant (BIG CHEMIE's "BYK-360") and a photoinitiator (IGM Resins' "Omnirad907") were added to this solution 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 (ZEON's "Zeonoa Film", 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 240 nm, and heated at 100 °C for 3 minutes to orient the liquid crystal. After cooling to room temperature, in a nitrogen atmosphere, the integrated light quantity was 400 mJ / cm 2The obtained long laminated body having a structure of a substrate / 1st liquid crystal alignment cured layer was subjected to photocuring by irradiating ultraviolet rays, and had a homogeneous alignment. The thickness of the 1st liquid crystal alignment cured layer was 2.0 μm, and the direction of the slow axis thereof was 15°. A long laminated body of a substrate / 2nd liquid crystal alignment cured layer (homogeneous alignment, thickness 1.0 μm, Re(550)=120 nm) was obtained in the same manner as above except that the coating thickness was changed. The direction of the slow axis of the 2nd liquid crystal alignment cured layer was 75°.

Chemical formula

[0074] 3. Fabrication of the optical laminate After laminating the 1st liquid crystal alignment cured layer via an acrylic adhesive (thickness 10 μm) on the surface of the TAC film of the polarizing plate, the substrate was peeled off. Next, the 2nd liquid crystal alignment cured layer was laminated via the adhesive A3 (thickness 1 μm) of Production Example 3 on the surface of the 1st liquid crystal alignment cured layer, and the substrate was peeled off to obtain a long optical laminate having a structure of a polarizing plate / 1st liquid crystal alignment cured layer / adhesive layer / 2nd liquid crystal alignment cured layer. Lamination and peeling were performed by a roll-to-roll process. The average refractive index of each of the 1st liquid crystal alignment cured layer and the 2nd liquid crystal alignment cured layer was 1.59. In the obtained optical laminate, the refractive index n of the 1st liquid crystal alignment cured layer in the direction of the transmission axis of the polarizer LC1 was 1.54, and the refractive index n of the 2nd liquid crystal alignment cured layer LC2 was 1.65. Further, the refractive index n of the adhesive layer AD was 1.56, and as a result, the display unevenness parameter was 0.007.

[0075] 4. Fabrication of the 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., trade name “Galaxy (registered trademark) A41”) were removed, and after cleaning the removal surface, the 2nd liquid crystal alignment cured layer side of the optical laminate obtained above was laminated via an acrylic adhesive (thickness 10 μm) on the cleaned surface to obtain an image display device. The obtained image display device was subjected to the above “linear unevenness” evaluation. The results are shown in Table 1.

[0076] [Examples 2 to 3 and Comparative Examples 1 to 2] An optical laminate and an image display device were obtained in the same manner as in Example 1 except that the configuration of the adhesive 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.

[0077] [Example 4] 1. Production of polarizing plate A polarizing plate was produced in the same manner as in Example 1.

[0078] 2. Production of retardation layer 2-1. Production of first liquid crystal alignment cured layer Using the same photopolymerizable liquid crystal compound as in Example 1, a long laminate having a structure of substrate / first liquid crystal alignment cured layer (Re(550)=144 nm) was obtained in the same manner as in Example 1. The first liquid crystal alignment cured layer was homogeneously aligned, and its thickness was 1.2 μm. The slow axis direction of the first liquid crystal alignment cured layer was 45°. 2-2. Production of second liquid crystal alignment cured layer 20 parts by weight of a side-chain liquid crystal polymer represented by the following chemical formula (n = 0.35, 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 photopolymerization initiator (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 by 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 laminate having a structure of substrate / second liquid crystal alignment cured layer (positive C plate, thickness 1.0 μm). [Chemical formula]

[0079] 3. Production of optical laminate and image display device Except for using the first liquid crystal alignment cured layer and the second liquid crystal alignment cured layer obtained above, and using the adhesive A1 (thickness 1 μm) of Production Example 1, in the same manner as in Example 1, a long optical laminate having a configuration of polarizing plate / first liquid crystal alignment cured layer / adhesive layer / second liquid crystal alignment cured layer was obtained. 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 1.59, and the refractive index n of the second liquid crystal alignment cured layer LC2 was 1.53. Further, the refractive index n of the adhesive layer AD was 1.50, and as a result, the display unevenness parameter was 0.009. An image display device was obtained in the same manner as in Example 1 except for using this optical laminate. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0080] [Examples 5 to 8] Optical laminates and image display devices were obtained in the same manner as in Example 4 except that the configuration of the adhesive layer was changed as shown in Table 1. The obtained image display devices were subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0081] [Example 9] An optical laminate was produced in the same manner as in Example 1 except that the slow axis direction of the first liquid crystal alignment cured layer was 75° and the slow axis direction of the second liquid crystal alignment cured layer was 15°. 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 adhesive layer AD was 1.56, and as a result, the display unevenness parameter was 0.007. An image display device was obtained in the same manner as in Example 1 except for using this optical laminate. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0082] [Examples 10 to 11 and Comparative Examples 3 to 4] An optical laminate and an image display device were obtained in the same manner as in Example 9, except that the configuration of the subsequent 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.

[0083] [Example 12] 1. Production of polarizing plate A polarizing plate was produced in the same manner as in Example 1.

[0084] 2. Production of retardation layer 2-1. Production of the first liquid crystal alignment cured layer Using the same photopolymerizable liquid crystal compound as in Example 1, a long laminate having the structure of substrate / first liquid crystal alignment cured layer (Re(550)=120 nm) was obtained in the same manner as in Example 1. The first liquid crystal alignment cured layer was homogeneously aligned, and its thickness was 1.0 μm. The slow axis direction of the first liquid crystal alignment cured layer was the 90° direction. 2-2. Production of the second liquid crystal alignment cured layer In the same manner as in Example 4, a long laminate having the structure of substrate / second liquid crystal alignment cured layer (positive C-plate) was obtained.

[0085] 3. Production of optical laminate A long optical laminate having the 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 liquid crystal alignment cured layer and the second liquid crystal alignment cured layer obtained above were used. In the obtained optical laminate, the refractive index n LC1 of the first liquid crystal alignment cured layer in the transmission axis direction of the polarizer was 1.65, and the refractive index n LC2 of the second liquid crystal alignment cured layer was 1.53. Further, the refractive index n AD of the adhesive layer was 1.56, and as a result, the display unevenness parameter was 0.009.

[0086] 4. Production 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., product 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 same evaluation as in Example 1. The results are shown in Table 1.

[0087] [Examples 13 to 14 and Comparative Examples 5 to 6] An optical laminate and an image display device were obtained in the same manner as in Example 12 except that the configuration of the adhesive 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.

[0088] [Example 15] An optical laminate was produced in the same manner as in Example 12 except that the arrangement order of the first liquid crystal alignment cured layer and the second liquid crystal alignment cured layer was reversed, the slow axis direction of the second liquid crystal alignment cured layer was set to the 0° direction, and the adhesive A1 (thickness: 1 μm) of Production Example 1 was used. In the obtained optical laminate, the refractive index n LC1 of the first liquid crystal alignment cured layer in the transmission axis direction of the polarizer was 1.53, and the refractive index n LC2 of the second liquid crystal alignment cured layer was 1.53. Furthermore, the refractive index n AD of the adhesive layer was 1.50, and as a result, the display unevenness parameter was 0.002. An image display device was obtained in the same manner as in Example 12 except that this optical laminate was used. The obtained image display device was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0089] [Examples 16 to 18 and Comparative Example 7] An optical laminate and an image display device were obtained in the same manner as in Example 15 except that the configuration of the adhesive 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.

[0090]

Table 1

[0091] In Table 1, for example, "Ex. 1" means Example 1, and "Comp. 1" means Comparative Example 1. Also, "Posi A" means a positive A plate, and "Posi C" means a positive C plate.

Industrial Applicability

[0092] The optical laminate according to the embodiment of the present invention can be suitably used in an image display device (typically, a liquid crystal display device or an organic EL display device).

Explanation of Reference Numerals

[0093] 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 25 Adhesive layer 100 Optical laminate

Claims

1. A polarizing plate including a polarizer and a retardation layer, wherein the retardation layer includes, in order from the polarizer side, a first liquid crystal alignment cured layer and a second liquid crystal alignment cured layer laminated to the first liquid crystal alignment cured layer via an adhesive layer. The refractive index n in the transmission axis direction of the polarizer of the first liquid crystal alignment cured layer ＬＣ１ , the refractive index n in the transmission axis direction of the polarizer of the second liquid crystal alignment cured layer ＬＣ２ , and the refractive index n in the transmission axis direction of the polarizer of the adhesive layer ＡＤ satisfy the following formula (1), an optical laminate: (n ＬＣ１ - n ＡＤ ) ２ +(n ＬＣ２ - n ＡＤ ) ２ < 0.01...(1).

2. The optical laminate according to Claim 1, which satisfies the following formula (2): (n ＬＣ１ - n ＡＤ ) ２ +(n ＬＣ２ - n ＡＤ ) ２ < 0.006... (2).

3. the said n ＬＣ１ or the said n ＬＣ２ is greater than 1.

60. The optical laminate according to claim 1.

4. The optical laminate according to Claim 1, wherein both the first liquid crystal alignment cured layer and the second liquid crystal alignment cured layer exhibit a refractive index characteristic of nx > ny.

5. The thickness T of the adhesive layer ＡＤ The optical laminate according to claim 1, wherein the thickness is 0.4 μm to 2.0 μm.

6. The optical laminate according to Claim 5, wherein the adhesive layer is composed of an active energy ray curable adhesive.

7. An image display device including the optical laminate according to any one of Claims 1 to 6.

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